1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 #![allow(non_snake_case)]
13 // Error messages for EXXXX errors.
14 // Each message should start and end with a new line, and be wrapped to 80 characters.
15 // In vim you can `:set tw=80` and use `gq` to wrap paragraphs. Use `:set tw=0` to disable.
16 register_long_diagnostics! {
19 This error suggests that the expression arm corresponding to the noted pattern
20 will never be reached as for all possible values of the expression being
21 matched, one of the preceding patterns will match.
23 This means that perhaps some of the preceding patterns are too general, this one
24 is too specific or the ordering is incorrect.
26 For example, the following `match` block has too many arms:
30 Some(bar) => {/* ... */}
32 _ => {/* ... */} // All possible cases have already been handled
36 `match` blocks have their patterns matched in order, so, for example, putting
37 a wildcard arm above a more specific arm will make the latter arm irrelevant.
39 Ensure the ordering of the match arm is correct and remove any superfluous
44 This error indicates that an empty match expression is invalid because the type
45 it is matching on is non-empty (there exist values of this type). In safe code
46 it is impossible to create an instance of an empty type, so empty match
47 expressions are almost never desired. This error is typically fixed by adding
48 one or more cases to the match expression.
50 An example of an empty type is `enum Empty { }`. So, the following will work:
63 fn foo(x: Option<String>) {
72 Not-a-Number (NaN) values cannot be compared for equality and hence can never
73 match the input to a match expression. So, the following will not compile:
76 const NAN: f32 = 0.0 / 0.0;
84 To match against NaN values, you should instead use the `is_nan()` method in a
90 x if x.is_nan() => { /* ... */ }
97 This error indicates that the compiler cannot guarantee a matching pattern for
98 one or more possible inputs to a match expression. Guaranteed matches are
99 required in order to assign values to match expressions, or alternatively,
100 determine the flow of execution.
102 If you encounter this error you must alter your patterns so that every possible
103 value of the input type is matched. For types with a small number of variants
104 (like enums) you should probably cover all cases explicitly. Alternatively, the
105 underscore `_` wildcard pattern can be added after all other patterns to match
110 Patterns used to bind names must be irrefutable, that is, they must guarantee
111 that a name will be extracted in all cases. If you encounter this error you
112 probably need to use a `match` or `if let` to deal with the possibility of
117 This error indicates that the bindings in a match arm would require a value to
118 be moved into more than one location, thus violating unique ownership. Code like
119 the following is invalid as it requires the entire `Option<String>` to be moved
120 into a variable called `op_string` while simultaneously requiring the inner
121 String to be moved into a variable called `s`.
124 let x = Some("s".to_string());
126 op_string @ Some(s) => ...
135 Names bound in match arms retain their type in pattern guards. As such, if a
136 name is bound by move in a pattern, it should also be moved to wherever it is
137 referenced in the pattern guard code. Doing so however would prevent the name
138 from being available in the body of the match arm. Consider the following:
141 match Some("hi".to_string()) {
142 Some(s) if s.len() == 0 => // use s.
147 The variable `s` has type `String`, and its use in the guard is as a variable of
148 type `String`. The guard code effectively executes in a separate scope to the
149 body of the arm, so the value would be moved into this anonymous scope and
150 therefore become unavailable in the body of the arm. Although this example seems
151 innocuous, the problem is most clear when considering functions that take their
155 match Some("hi".to_string()) {
156 Some(s) if { drop(s); false } => (),
162 The value would be dropped in the guard then become unavailable not only in the
163 body of that arm but also in all subsequent arms! The solution is to bind by
164 reference when using guards or refactor the entire expression, perhaps by
165 putting the condition inside the body of the arm.
169 In a pattern, all values that don't implement the `Copy` trait have to be bound
170 the same way. The goal here is to avoid binding simultaneously by-move and
173 This limitation may be removed in a future version of Rust.
180 let x = Some((X { x: () }, X { x: () }));
182 Some((y, ref z)) => {},
187 You have two solutions:
189 Solution #1: Bind the pattern's values the same way.
194 let x = Some((X { x: () }, X { x: () }));
196 Some((ref y, ref z)) => {},
197 // or Some((y, z)) => {}
202 Solution #2: Implement the `Copy` trait for the `X` structure.
204 However, please keep in mind that the first solution should be preferred.
207 #[derive(Clone, Copy)]
210 let x = Some((X { x: () }, X { x: () }));
212 Some((y, ref z)) => {},
219 The value of statics and constants must be known at compile time, and they live
220 for the entire lifetime of a program. Creating a boxed value allocates memory on
221 the heap at runtime, and therefore cannot be done at compile time. Erroneous
225 #![feature(box_syntax)]
227 const CON : Box<i32> = box 0;
232 Initializers for constants and statics are evaluated at compile time.
233 User-defined operators rely on user-defined functions, which cannot be evaluated
243 impl Index<u8> for Foo {
246 fn index<'a>(&'a self, idx: u8) -> &'a u8 { &self.a }
249 const a: Foo = Foo { a: 0u8 };
250 const b: u8 = a[0]; // Index trait is defined by the user, bad!
253 Only operators on builtin types are allowed.
258 const a: &'static [i32] = &[1, 2, 3];
259 const b: i32 = a[0]; // Good!
264 Static and const variables can refer to other const variables. But a const
265 variable cannot refer to a static variable. For example, `Y` cannot refer to `X`
273 To fix this, the value can be extracted as a const and then used:
283 Constants can only be initialized by a constant value or, in a future
284 version of Rust, a call to a const function. This error indicates the use
285 of a path (like a::b, or x) denoting something other than one of these
286 allowed items. Example:
289 const FOO: i32 = { let x = 0; x }; // 'x' isn't a constant nor a function!
292 To avoid it, you have to replace the non-constant value:
295 const FOO: i32 = { const X : i32 = 0; X };
297 const FOO: i32 = { 0 }; // but brackets are useless here
301 // FIXME(#24111) Change the language here when const fn stabilizes
303 The only functions that can be called in static or constant expressions are
304 `const` functions, and struct/enum constructors. `const` functions are only
305 available on a nightly compiler. Rust currently does not support more general
306 compile-time function execution.
309 const FOO: Option<u8> = Some(1); // enum constructor
311 const BAR: Bar = Bar {x: 1}; // struct constructor
314 See [RFC 911] for more details on the design of `const fn`s.
316 [RFC 911]: https://github.com/rust-lang/rfcs/blob/master/text/0911-const-fn.md
320 References in statics and constants may only refer to immutable values. Example:
326 // these three are not allowed:
327 const CR: &'static mut i32 = &mut C;
328 static STATIC_REF: &'static mut i32 = &mut X;
329 static CONST_REF: &'static mut i32 = &mut C;
332 Statics are shared everywhere, and if they refer to mutable data one might
333 violate memory safety since holding multiple mutable references to shared data
336 If you really want global mutable state, try using `static mut` or a global
341 The value of static and const variables must be known at compile time. You
342 can't cast a pointer as an integer because we can't know what value the
345 However, pointers to other constants' addresses are allowed in constants,
350 const Y: *const u32 = &X;
353 Therefore, casting one of these non-constant pointers to an integer results
354 in a non-constant integer which lead to this error. Example:
358 const Y: usize = &X as *const u32 as usize;
364 A function call isn't allowed in the const's initialization expression
365 because the expression's value must be known at compile-time. Example of
374 fn test(&self) -> i32 {
380 const FOO: Test = Test::V1;
382 const A: i32 = FOO.test(); // You can't call Test::func() here !
386 Remember: you can't use a function call inside a const's initialization
387 expression! However, you can totally use it anywhere else:
391 const FOO: Test = Test::V1;
393 FOO.func(); // here is good
394 let x = FOO.func(); // or even here!
400 This error indicates that an attempt was made to divide by zero (or take the
401 remainder of a zero divisor) in a static or constant expression. Erroneous
405 const X: i32 = 42 / 0;
406 // error: attempted to divide by zero in a constant expression
411 When matching against a range, the compiler verifies that the range is
412 non-empty. Range patterns include both end-points, so this is equivalent to
413 requiring the start of the range to be less than or equal to the end of the
420 // This range is ok, albeit pointless.
422 // This range is empty, and the compiler can tell.
429 Trait objects like `Box<Trait>` can only be constructed when certain
430 requirements are satisfied by the trait in question.
432 Trait objects are a form of dynamic dispatch and use a dynamically sized type
433 for the inner type. So, for a given trait `Trait`, when `Trait` is treated as a
434 type, as in `Box<Trait>`, the inner type is 'unsized'. In such cases the boxed
435 pointer is a 'fat pointer' that contains an extra pointer to a table of methods
436 (among other things) for dynamic dispatch. This design mandates some
437 restrictions on the types of traits that are allowed to be used in trait
438 objects, which are collectively termed as 'object safety' rules.
440 Attempting to create a trait object for a non object-safe trait will trigger
443 There are various rules:
445 ### The trait cannot require `Self: Sized`
447 When `Trait` is treated as a type, the type does not implement the special
448 `Sized` trait, because the type does not have a known size at compile time and
449 can only be accessed behind a pointer. Thus, if we have a trait like the
453 trait Foo where Self: Sized {
458 we cannot create an object of type `Box<Foo>` or `&Foo` since in this case
459 `Self` would not be `Sized`.
461 Generally, `Self : Sized` is used to indicate that the trait should not be used
462 as a trait object. If the trait comes from your own crate, consider removing
465 ### Method references the `Self` type in its arguments or return type
467 This happens when a trait has a method like the following:
471 fn foo(&self) -> Self;
474 impl Trait for String {
475 fn foo(&self) -> Self {
481 fn foo(&self) -> Self {
487 (Note that `&self` and `&mut self` are okay, it's additional `Self` types which
490 In such a case, the compiler cannot predict the return type of `foo()` in a
491 situation like the following:
494 fn call_foo(x: Box<Trait>) {
495 let y = x.foo(); // What type is y?
500 If only some methods aren't object-safe, you can add a `where Self: Sized` bound
501 on them to mark them as explicitly unavailable to trait objects. The
502 functionality will still be available to all other implementers, including
503 `Box<Trait>` which is itself sized (assuming you `impl Trait for Box<Trait>`).
507 fn foo(&self) -> Self where Self: Sized;
512 Now, `foo()` can no longer be called on a trait object, but you will now be
513 allowed to make a trait object, and that will be able to call any object-safe
514 methods". With such a bound, one can still call `foo()` on types implementing
515 that trait that aren't behind trait objects.
517 ### Method has generic type parameters
519 As mentioned before, trait objects contain pointers to method tables. So, if we
526 impl Trait for String {
539 At compile time each implementation of `Trait` will produce a table containing
540 the various methods (and other items) related to the implementation.
542 This works fine, but when the method gains generic parameters, we can have a
545 Usually, generic parameters get _monomorphized_. For example, if I have
553 the machine code for `foo::<u8>()`, `foo::<bool>()`, `foo::<String>()`, or any
554 other type substitution is different. Hence the compiler generates the
555 implementation on-demand. If you call `foo()` with a `bool` parameter, the
556 compiler will only generate code for `foo::<bool>()`. When we have additional
557 type parameters, the number of monomorphized implementations the compiler
558 generates does not grow drastically, since the compiler will only generate an
559 implementation if the function is called with unparametrized substitutions
560 (i.e., substitutions where none of the substituted types are themselves
563 However, with trait objects we have to make a table containing _every_ object
564 that implements the trait. Now, if it has type parameters, we need to add
565 implementations for every type that implements the trait, and there could
566 theoretically be an infinite number of types.
572 fn foo<T>(&self, on: T);
575 impl Trait for String {
576 fn foo<T>(&self, on: T) {
581 fn foo<T>(&self, on: T) {
585 // 8 more implementations
588 Now, if we have the following code:
591 fn call_foo(thing: Box<Trait>) {
592 thing.foo(true); // this could be any one of the 8 types above
598 we don't just need to create a table of all implementations of all methods of
599 `Trait`, we need to create such a table, for each different type fed to
600 `foo()`. In this case this turns out to be (10 types implementing `Trait`)*(3
601 types being fed to `foo()`) = 30 implementations!
603 With real world traits these numbers can grow drastically.
605 To fix this, it is suggested to use a `where Self: Sized` bound similar to the
606 fix for the sub-error above if you do not intend to call the method with type
611 fn foo<T>(&self, on: T) where Self: Sized;
616 If this is not an option, consider replacing the type parameter with another
617 trait object (e.g. if `T: OtherTrait`, use `on: Box<OtherTrait>`). If the number
618 of types you intend to feed to this method is limited, consider manually listing
619 out the methods of different types.
621 ### Method has no receiver
623 Methods that do not take a `self` parameter can't be called since there won't be
624 a way to get a pointer to the method table for them
632 This could be called as `<Foo as Foo>::foo()`, which would not be able to pick
635 Adding a `Self: Sized` bound to these methods will generally make this compile.
639 fn foo() -> u8 where Self: Sized;
643 ### The trait cannot use `Self` as a type parameter in the supertrait listing
645 This is similar to the second sub-error, but subtler. It happens in situations
651 trait Trait: Super<Self> {
656 impl Super<Foo> for Foo{}
658 impl Trait for Foo {}
661 Here, the supertrait might have methods as follows:
665 fn get_a(&self) -> A; // note that this is object safe!
669 If the trait `Foo` was deriving from something like `Super<String>` or
670 `Super<T>` (where `Foo` itself is `Foo<T>`), this is okay, because given a type
671 `get_a()` will definitely return an object of that type.
673 However, if it derives from `Super<Self>`, even though `Super` is object safe,
674 the method `get_a()` would return an object of unknown type when called on the
675 function. `Self` type parameters let us make object safe traits no longer safe,
676 so they are forbidden when specifying supertraits.
678 There's no easy fix for this, generally code will need to be refactored so that
679 you no longer need to derive from `Super<Self>`.
683 You tried to give a type parameter to a type which doesn't need it. Erroneous
687 type X = u32<i32>; // error: type parameters are not allowed on this type
690 Please check that you used the correct type and recheck its definition. Perhaps
691 it doesn't need the type parameter.
696 type X = u32; // this compiles
699 Note that type parameters for enum-variant constructors go after the variant,
700 not after the enum (Option::None::<u32>, not Option::<u32>::None).
704 You tried to give a lifetime parameter to a type which doesn't need it.
705 Erroneous code example:
708 type X = u32<'static>; // error: lifetime parameters are not allowed on
712 Please check that the correct type was used and recheck its definition; perhaps
713 it doesn't need the lifetime parameter. Example:
721 Using unsafe functionality, is potentially dangerous and disallowed
722 by safety checks. Examples:
724 - Dereferencing raw pointers
725 - Calling functions via FFI
726 - Calling functions marked unsafe
728 These safety checks can be relaxed for a section of the code
729 by wrapping the unsafe instructions with an `unsafe` block. For instance:
732 unsafe fn f() { return; }
739 See also https://doc.rust-lang.org/book/unsafe.html
742 // This shouldn't really ever trigger since the repeated value error comes first
744 A binary can only have one entry point, and by default that entry point is the
745 function `main()`. If there are multiple such functions, please rename one.
749 This error indicates that the compiler found multiple functions with the
750 `#[main]` attribute. This is an error because there must be a unique entry
751 point into a Rust program.
755 This error indicates that the compiler found multiple functions with the
756 `#[start]` attribute. This is an error because there must be a unique entry
757 point into a Rust program.
760 // FIXME link this to the relevant turpl chapters for instilling fear of the
761 // transmute gods in the user
763 There are various restrictions on transmuting between types in Rust; for example
764 types being transmuted must have the same size. To apply all these restrictions,
765 the compiler must know the exact types that may be transmuted. When type
766 parameters are involved, this cannot always be done.
768 So, for example, the following is not allowed:
771 struct Foo<T>(Vec<T>)
773 fn foo<T>(x: Vec<T>) {
774 // we are transmuting between Vec<T> and Foo<T> here
775 let y: Foo<T> = unsafe { transmute(x) };
776 // do something with y
780 In this specific case there's a good chance that the transmute is harmless (but
781 this is not guaranteed by Rust). However, when alignment and enum optimizations
782 come into the picture, it's quite likely that the sizes may or may not match
783 with different type parameter substitutions. It's not possible to check this for
784 _all_ possible types, so `transmute()` simply only accepts types without any
785 unsubstituted type parameters.
787 If you need this, there's a good chance you're doing something wrong. Keep in
788 mind that Rust doesn't guarantee much about the layout of different structs
789 (even two structs with identical declarations may have different layouts). If
790 there is a solution that avoids the transmute entirely, try it instead.
792 If it's possible, hand-monomorphize the code by writing the function for each
793 possible type substitution. It's possible to use traits to do this cleanly,
797 trait MyTransmutableType {
798 fn transmute(Vec<Self>) -> Foo<Self>
801 impl MyTransmutableType for u8 {
802 fn transmute(x: Foo<u8>) -> Vec<u8> {
806 impl MyTransmutableType for String {
807 fn transmute(x: Foo<String>) -> Vec<String> {
811 // ... more impls for the types you intend to transmute
813 fn foo<T: MyTransmutableType>(x: Vec<T>) {
814 let y: Foo<T> = <T as MyTransmutableType>::transmute(x);
815 // do something with y
819 Each impl will be checked for a size match in the transmute as usual, and since
820 there are no unbound type parameters involved, this should compile unless there
821 is a size mismatch in one of the impls.
823 It is also possible to manually transmute:
826 ptr::read(&v as *const _ as *const SomeType) // `v` transmuted to `SomeType`
829 Note that this does not move `v` (unlike `transmute`), and may need a
830 call to `mem::forget(v)` in case you want to avoid destructors being called.
834 Lang items are already implemented in the standard library. Unless you are
835 writing a free-standing application (e.g. a kernel), you do not need to provide
838 You can build a free-standing crate by adding `#![no_std]` to the crate
845 See also https://doc.rust-lang.org/book/no-stdlib.html
849 `const` and `static` mean different things. A `const` is a compile-time
850 constant, an alias for a literal value. This property means you can match it
851 directly within a pattern.
853 The `static` keyword, on the other hand, guarantees a fixed location in memory.
854 This does not always mean that the value is constant. For example, a global
855 mutex can be declared `static` as well.
857 If you want to match against a `static`, consider using a guard instead:
860 static FORTY_TWO: i32 = 42;
862 Some(x) if x == FORTY_TWO => ...
869 In Rust, you can only move a value when its size is known at compile time.
871 To work around this restriction, consider "hiding" the value behind a reference:
872 either `&x` or `&mut x`. Since a reference has a fixed size, this lets you move
877 An if-let pattern attempts to match the pattern, and enters the body if the
878 match was successful. If the match is irrefutable (when it cannot fail to
879 match), use a regular `let`-binding instead. For instance:
882 struct Irrefutable(i32);
883 let irr = Irrefutable(0);
885 // This fails to compile because the match is irrefutable.
886 if let Irrefutable(x) = irr {
887 // This body will always be executed.
892 let Irrefutable(x) = irr;
898 A while-let pattern attempts to match the pattern, and enters the body if the
899 match was successful. If the match is irrefutable (when it cannot fail to
900 match), use a regular `let`-binding inside a `loop` instead. For instance:
903 struct Irrefutable(i32);
904 let irr = Irrefutable(0);
906 // This fails to compile because the match is irrefutable.
907 while let Irrefutable(x) = irr {
913 let Irrefutable(x) = irr;
920 Enum variants are qualified by default. For example, given this type:
929 you would match it using:
938 If you don't qualify the names, the code will bind new variables named "GET" and
939 "POST" instead. This behavior is likely not what you want, so `rustc` warns when
942 Qualified names are good practice, and most code works well with them. But if
943 you prefer them unqualified, you can import the variants into scope:
947 enum Method { GET, POST }
950 If you want others to be able to import variants from your module directly, use
955 enum Method { GET, POST }
960 An associated type binding was done outside of the type parameter declaration
961 and `where` clause. Erroneous code example:
966 fn boo(&self) -> <Self as Foo>::A;
973 fn boo(&self) -> usize { 42 }
976 fn baz<I>(x: &<I as Foo<A=Bar>>::A) {}
977 // error: associated type bindings are not allowed here
980 To solve this error, please move the type bindings in the type parameter
984 fn baz<I: Foo<A=Bar>>(x: &<I as Foo>::A) {} // ok!
987 or in the `where` clause:
990 fn baz<I>(x: &<I as Foo>::A) where I: Foo<A=Bar> {}
995 When using a lifetime like `'a` in a type, it must be declared before being
998 These two examples illustrate the problem:
1001 // error, use of undeclared lifetime name `'a`
1002 fn foo(x: &'a str) { }
1005 // error, use of undeclared lifetime name `'a`
1010 These can be fixed by declaring lifetime parameters:
1013 fn foo<'a>(x: &'a str) { }
1022 Declaring certain lifetime names in parameters is disallowed. For example,
1023 because the `'static` lifetime is a special built-in lifetime name denoting
1024 the lifetime of the entire program, this is an error:
1027 // error, invalid lifetime parameter name `'static`
1028 fn foo<'static>(x: &'static str) { }
1033 A lifetime name cannot be declared more than once in the same scope. For
1037 // error, lifetime name `'a` declared twice in the same scope
1038 fn foo<'a, 'b, 'a>(x: &'a str, y: &'b str) { }
1043 An unknown external lang item was used. Erroneous code example:
1046 #![feature(lang_items)]
1049 #[lang = "cake"] // error: unknown external lang item: `cake`
1054 A list of available external lang items is available in
1055 `src/librustc/middle/weak_lang_items.rs`. Example:
1058 #![feature(lang_items)]
1061 #[lang = "panic_fmt"] // ok!
1068 This error indicates that a static or constant references itself.
1069 All statics and constants need to resolve to a value in an acyclic manner.
1071 For example, neither of the following can be sensibly compiled:
1084 This error indicates the use of a loop keyword (`break` or `continue`) inside a
1085 closure but outside of any loop. Erroneous code example:
1088 let w = || { break; }; // error: `break` inside of a closure
1091 `break` and `continue` keywords can be used as normal inside closures as long as
1092 they are also contained within a loop. To halt the execution of a closure you
1093 should instead use a return statement. Example:
1107 This error indicates the use of a loop keyword (`break` or `continue`) outside
1108 of a loop. Without a loop to break out of or continue in, no sensible action can
1109 be taken. Erroneous code example:
1113 break; // error: `break` outside of loop
1117 Please verify that you are using `break` and `continue` only in loops. Example:
1129 Functions must eventually return a value of their return type. For example, in
1130 the following function
1133 fn foo(x: u8) -> u8 {
1135 x // alternatively, `return x`
1141 if the condition is true, the value `x` is returned, but if the condition is
1142 false, control exits the `if` block and reaches a place where nothing is being
1143 returned. All possible control paths must eventually return a `u8`, which is not
1146 An easy fix for this in a complicated function is to specify a default return
1150 fn foo(x: u8) -> u8 {
1152 x // alternatively, `return x`
1154 // lots of other if branches
1155 0 // return 0 if all else fails
1159 It is advisable to find out what the unhandled cases are and check for them,
1160 returning an appropriate value or panicking if necessary.
1164 Rust lets you define functions which are known to never return, i.e. are
1165 'diverging', by marking its return type as `!`.
1167 For example, the following functions never return:
1175 foo() // foo() is diverging, so this will diverge too
1179 panic!(); // this macro internally expands to a call to a diverging function
1184 Such functions can be used in a place where a value is expected without
1185 returning a value of that type, for instance:
1191 _ => foo() // diverging function called here
1196 If the third arm of the match block is reached, since `foo()` doesn't ever
1197 return control to the match block, it is fine to use it in a place where an
1198 integer was expected. The `match` block will never finish executing, and any
1199 point where `y` (like the print statement) is needed will not be reached.
1201 However, if we had a diverging function that actually does finish execution
1209 then we would have an unknown value for `y` in the following code:
1220 In the previous example, the print statement was never reached when the wildcard
1221 match arm was hit, so we were okay with `foo()` not returning an integer that we
1222 could set to `y`. But in this example, `foo()` actually does return control, so
1223 the print statement will be executed with an uninitialized value.
1225 Obviously we cannot have functions which are allowed to be used in such
1226 positions and yet can return control. So, if you are defining a function that
1227 returns `!`, make sure that there is no way for it to actually finish executing.
1231 This is because of a type mismatch between the associated type of some
1232 trait (e.g. `T::Bar`, where `T` implements `trait Quux { type Bar; }`)
1233 and another type `U` that is required to be equal to `T::Bar`, but is not.
1236 Here is a basic example:
1239 trait Trait { type AssociatedType; }
1240 fn foo<T>(t: T) where T: Trait<AssociatedType=u32> {
1243 impl Trait for i8 { type AssociatedType = &'static str; }
1247 Here is that same example again, with some explanatory comments:
1250 trait Trait { type AssociatedType; }
1252 fn foo<T>(t: T) where T: Trait<AssociatedType=u32> {
1253 // ~~~~~~~~ ~~~~~~~~~~~~~~~~~~
1255 // This says `foo` can |
1256 // only be used with |
1258 // implements `Trait`. |
1260 // This says not only must
1261 // `T` be an impl of `Trait`
1262 // but also that the impl
1263 // must assign the type `u32`
1264 // to the associated type.
1268 impl Trait for i8 { type AssociatedType = &'static str; }
1269 ~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1274 // ... but it is an implementation
1275 // that assigns `&'static str` to
1276 // the associated type.
1279 // Here, we invoke `foo` with an `i8`, which does not satisfy
1280 // the constraint `<i8 as Trait>::AssociatedType=u32`, and
1281 // therefore the type-checker complains with this error code.
1284 Here is a more subtle instance of the same problem, that can
1285 arise with for-loops in Rust:
1288 let vs: Vec<i32> = vec![1, 2, 3, 4];
1297 The above fails because of an analogous type mismatch,
1298 though may be harder to see. Again, here are some
1299 explanatory comments for the same example:
1303 let vs = vec![1, 2, 3, 4];
1305 // `for`-loops use a protocol based on the `Iterator`
1306 // trait. Each item yielded in a `for` loop has the
1307 // type `Iterator::Item` -- that is, `Item` is the
1308 // associated type of the concrete iterator impl.
1312 // | We borrow `vs`, iterating over a sequence of
1313 // | *references* of type `&Elem` (where `Elem` is
1314 // | vector's element type). Thus, the associated
1315 // | type `Item` must be a reference `&`-type ...
1317 // ... and `v` has the type `Iterator::Item`, as dictated by
1318 // the `for`-loop protocol ...
1324 // ... but *here*, `v` is forced to have some integral type;
1325 // only types like `u8`,`i8`,`u16`,`i16`, et cetera can
1326 // match the pattern `1` ...
1331 // ... therefore, the compiler complains, because it sees
1332 // an attempt to solve the equations
1333 // `some integral-type` = type-of-`v`
1334 // = `Iterator::Item`
1335 // = `&Elem` (i.e. `some reference type`)
1337 // which cannot possibly all be true.
1343 To avoid those issues, you have to make the types match correctly.
1344 So we can fix the previous examples like this:
1348 trait Trait { type AssociatedType; }
1349 fn foo<T>(t: T) where T: Trait<AssociatedType = &'static str> {
1352 impl Trait for i8 { type AssociatedType = &'static str; }
1355 // For-Loop Example:
1356 let vs = vec![1, 2, 3, 4];
1367 The `#[rustc_on_unimplemented]` attribute lets you specify a custom error
1368 message for when a particular trait isn't implemented on a type placed in a
1369 position that needs that trait. For example, when the following code is
1373 fn foo<T: Index<u8>>(x: T){}
1375 #[rustc_on_unimplemented = "the type `{Self}` cannot be indexed by `{Idx}`"]
1376 trait Index<Idx> { ... }
1378 foo(true); // `bool` does not implement `Index<u8>`
1381 there will be an error about `bool` not implementing `Index<u8>`, followed by a
1382 note saying "the type `bool` cannot be indexed by `u8`".
1384 As you can see, you can specify type parameters in curly braces for substitution
1385 with the actual types (using the regular format string syntax) in a given
1386 situation. Furthermore, `{Self}` will substitute to the type (in this case,
1387 `bool`) that we tried to use.
1389 This error appears when the curly braces contain an identifier which doesn't
1390 match with any of the type parameters or the string `Self`. This might happen if
1391 you misspelled a type parameter, or if you intended to use literal curly braces.
1392 If it is the latter, escape the curly braces with a second curly brace of the
1393 same type; e.g. a literal `{` is `{{`
1397 The `#[rustc_on_unimplemented]` attribute lets you specify a custom error
1398 message for when a particular trait isn't implemented on a type placed in a
1399 position that needs that trait. For example, when the following code is
1403 fn foo<T: Index<u8>>(x: T){}
1405 #[rustc_on_unimplemented = "the type `{Self}` cannot be indexed by `{Idx}`"]
1406 trait Index<Idx> { ... }
1408 foo(true); // `bool` does not implement `Index<u8>`
1411 there will be an error about `bool` not implementing `Index<u8>`, followed by a
1412 note saying "the type `bool` cannot be indexed by `u8`".
1414 As you can see, you can specify type parameters in curly braces for substitution
1415 with the actual types (using the regular format string syntax) in a given
1416 situation. Furthermore, `{Self}` will substitute to the type (in this case,
1417 `bool`) that we tried to use.
1419 This error appears when the curly braces do not contain an identifier. Please
1420 add one of the same name as a type parameter. If you intended to use literal
1421 braces, use `{{` and `}}` to escape them.
1425 The `#[rustc_on_unimplemented]` attribute lets you specify a custom error
1426 message for when a particular trait isn't implemented on a type placed in a
1427 position that needs that trait. For example, when the following code is
1431 fn foo<T: Index<u8>>(x: T){}
1433 #[rustc_on_unimplemented = "the type `{Self}` cannot be indexed by `{Idx}`"]
1434 trait Index<Idx> { ... }
1436 foo(true); // `bool` does not implement `Index<u8>`
1439 there will be an error about `bool` not implementing `Index<u8>`, followed by a
1440 note saying "the type `bool` cannot be indexed by `u8`".
1442 For this to work, some note must be specified. An empty attribute will not do
1443 anything, please remove the attribute or add some helpful note for users of the
1448 This error occurs when there was a recursive trait requirement that overflowed
1449 before it could be evaluated. Often this means that there is unbounded recursion
1450 in resolving some type bounds.
1452 For example, in the following code
1459 impl<T> Foo for T where Bar<T>: Foo {}
1462 to determine if a `T` is `Foo`, we need to check if `Bar<T>` is `Foo`. However,
1463 to do this check, we need to determine that `Bar<Bar<T>>` is `Foo`. To determine
1464 this, we check if `Bar<Bar<Bar<T>>>` is `Foo`, and so on. This is clearly a
1465 recursive requirement that can't be resolved directly.
1467 Consider changing your trait bounds so that they're less self-referential.
1471 This error occurs when a bound in an implementation of a trait does not match
1472 the bounds specified in the original trait. For example:
1480 fn foo<T>(x: T) where T: Copy {}
1484 Here, all types implementing `Foo` must have a method `foo<T>(x: T)` which can
1485 take any type `T`. However, in the `impl` for `bool`, we have added an extra
1486 bound that `T` is `Copy`, which isn't compatible with the original trait.
1488 Consider removing the bound from the method or adding the bound to the original
1489 method definition in the trait.
1493 You tried to use a type which doesn't implement some trait in a place which
1494 expected that trait. Erroneous code example:
1497 // here we declare the Foo trait with a bar method
1502 // we now declare a function which takes an object implementing the Foo trait
1503 fn some_func<T: Foo>(foo: T) {
1508 // we now call the method with the i32 type, which doesn't implement
1510 some_func(5i32); // error: the trait `Foo` is not implemented for the
1515 In order to fix this error, verify that the type you're using does implement
1523 fn some_func<T: Foo>(foo: T) {
1524 foo.bar(); // we can now use this method since i32 implements the
1528 // we implement the trait on the i32 type
1534 some_func(5i32); // ok!
1540 You tried to supply a type which doesn't implement some trait in a location
1541 which expected that trait. This error typically occurs when working with
1542 `Fn`-based types. Erroneous code example:
1545 fn foo<F: Fn()>(x: F) { }
1548 // type mismatch: the type ... implements the trait `core::ops::Fn<(_,)>`,
1549 // but the trait `core::ops::Fn<()>` is required (expected (), found tuple
1555 The issue in this case is that `foo` is defined as accepting a `Fn` with no
1556 arguments, but the closure we attempted to pass to it requires one argument.
1560 This error indicates that type inference did not result in one unique possible
1561 type, and extra information is required. In most cases this can be provided
1562 by adding a type annotation. Sometimes you need to specify a generic type
1565 A common example is the `collect` method on `Iterator`. It has a generic type
1566 parameter with a `FromIterator` bound, which for a `char` iterator is
1567 implemented by `Vec` and `String` among others. Consider the following snippet
1568 that reverses the characters of a string:
1571 let x = "hello".chars().rev().collect();
1574 In this case, the compiler cannot infer what the type of `x` should be:
1575 `Vec<char>` and `String` are both suitable candidates. To specify which type to
1576 use, you can use a type annotation on `x`:
1579 let x: Vec<char> = "hello".chars().rev().collect();
1582 It is not necessary to annotate the full type. Once the ambiguity is resolved,
1583 the compiler can infer the rest:
1586 let x: Vec<_> = "hello".chars().rev().collect();
1589 Another way to provide the compiler with enough information, is to specify the
1590 generic type parameter:
1593 let x = "hello".chars().rev().collect::<Vec<char>>();
1596 Again, you need not specify the full type if the compiler can infer it:
1599 let x = "hello".chars().rev().collect::<Vec<_>>();
1602 Apart from a method or function with a generic type parameter, this error can
1603 occur when a type parameter of a struct or trait cannot be inferred. In that
1604 case it is not always possible to use a type annotation, because all candidates
1605 have the same return type. For instance:
1609 // Some fields omitted.
1618 let number = Foo::bar();
1623 This will fail because the compiler does not know which instance of `Foo` to
1624 call `bar` on. Change `Foo::bar()` to `Foo::<T>::bar()` to resolve the error.
1628 This error occurs when the compiler doesn't have enough information
1629 to unambiguously choose an implementation.
1639 impl Generator for Impl {
1640 fn create() -> u32 { 1 }
1644 impl Generator for AnotherImpl {
1645 fn create() -> u32 { 2 }
1649 let cont: u32 = Generator::create();
1650 // error, impossible to choose one of Generator trait implementation
1651 // Impl or AnotherImpl? Maybe anything else?
1655 To resolve this error use the concrete type:
1659 let gen1 = AnotherImpl::create();
1661 // if there are multiple methods with same name (different traits)
1662 let gen2 = <AnotherImpl as Generator>::create();
1668 This error indicates that the given recursion limit could not be parsed. Ensure
1669 that the value provided is a positive integer between quotes, like so:
1672 #![recursion_limit="1000"]
1677 Patterns used to bind names must be irrefutable. That is, they must guarantee
1678 that a name will be extracted in all cases. Instead of pattern matching the
1679 loop variable, consider using a `match` or `if let` inside the loop body. For
1683 // This fails because `None` is not covered.
1688 // Match inside the loop instead:
1698 if let Some(x) = item {
1706 Mutable borrows are not allowed in pattern guards, because matching cannot have
1707 side effects. Side effects could alter the matched object or the environment
1708 on which the match depends in such a way, that the match would not be
1709 exhaustive. For instance, the following would not match any arm if mutable
1710 borrows were allowed:
1715 option if option.take().is_none() => { /* impossible, option is `Some` */ },
1716 Some(_) => { } // When the previous match failed, the option became `None`.
1722 Assignments are not allowed in pattern guards, because matching cannot have
1723 side effects. Side effects could alter the matched object or the environment
1724 on which the match depends in such a way, that the match would not be
1725 exhaustive. For instance, the following would not match any arm if assignments
1731 option if { option = None; false } { },
1732 Some(_) => { } // When the previous match failed, the option became `None`.
1738 In certain cases it is possible for sub-bindings to violate memory safety.
1739 Updates to the borrow checker in a future version of Rust may remove this
1740 restriction, but for now patterns must be rewritten without sub-bindings.
1744 match Some("hi".to_string()) {
1745 ref op_string_ref @ Some(ref s) => ...
1750 match Some("hi".to_string()) {
1752 let op_string_ref = &Some(s);
1759 The `op_string_ref` binding has type `&Option<&String>` in both cases.
1761 See also https://github.com/rust-lang/rust/issues/14587
1765 In an array literal `[x; N]`, `N` is the number of elements in the array. This
1766 number cannot be negative.
1770 The length of an array is part of its type. For this reason, this length must be
1771 a compile-time constant.
1775 This error occurs when the compiler was unable to infer the concrete type of a
1776 variable. It can occur for several cases, the most common of which is a
1777 mismatch in the expected type that the compiler inferred for a variable's
1778 initializing expression, and the actual type explicitly assigned to the
1784 let x: i32 = "I am not a number!";
1785 // ~~~ ~~~~~~~~~~~~~~~~~~~~
1787 // | initializing expression;
1788 // | compiler infers type `&str`
1790 // type `i32` assigned to variable `x`
1793 Another situation in which this occurs is when you attempt to use the `try!`
1794 macro inside a function that does not return a `Result<T, E>`:
1800 let mut f = try!(File::create("foo.txt"));
1804 This code gives an error like this:
1807 <std macros>:5:8: 6:42 error: mismatched types:
1809 found `core::result::Result<_, _>`
1811 found enum `core::result::Result`) [E0308]
1814 `try!` returns a `Result<T, E>`, and so the function must. But `main()` has
1815 `()` as its return type, hence the error.
1819 Types in type definitions have lifetimes associated with them that represent
1820 how long the data stored within them is guaranteed to be live. This lifetime
1821 must be as long as the data needs to be alive, and missing the constraint that
1822 denotes this will cause this error.
1825 // This won't compile because T is not constrained, meaning the data
1826 // stored in it is not guaranteed to last as long as the reference
1831 // This will compile, because it has the constraint on the type parameter
1832 struct Foo<'a, T: 'a> {
1839 Types in type definitions have lifetimes associated with them that represent
1840 how long the data stored within them is guaranteed to be live. This lifetime
1841 must be as long as the data needs to be alive, and missing the constraint that
1842 denotes this will cause this error.
1845 // This won't compile because T is not constrained to the static lifetime
1846 // the reference needs
1851 // This will compile, because it has the constraint on the type parameter
1852 struct Foo<T: 'static> {
1859 Method calls that aren't calls to inherent `const` methods are disallowed
1860 in statics, constants, and constant functions.
1865 const BAZ: i32 = Foo(25).bar(); // error, `bar` isn't `const`
1870 const fn foo(&self) -> i32 {
1871 self.bar() // error, `bar` isn't `const`
1874 fn bar(&self) -> i32 { self.0 }
1878 For more information about `const fn`'s, see [RFC 911].
1880 [RFC 911]: https://github.com/rust-lang/rfcs/blob/master/text/0911-const-fn.md
1886 > It is invalid for a static to reference another static by value. It is
1887 > required that all references be borrowed.
1889 [RFC 246]: https://github.com/rust-lang/rfcs/pull/246
1893 The value assigned to a constant expression must be known at compile time,
1894 which is not the case when comparing raw pointers. Erroneous code example:
1897 static foo: i32 = 42;
1898 static bar: i32 = 43;
1900 static baz: bool = { (&foo as *const i32) == (&bar as *const i32) };
1901 // error: raw pointers cannot be compared in statics!
1904 Please check that the result of the comparison can be determined at compile time
1905 or isn't assigned to a constant expression. Example:
1908 static foo: i32 = 42;
1909 static bar: i32 = 43;
1911 let baz: bool = { (&foo as *const i32) == (&bar as *const i32) };
1912 // baz isn't a constant expression so it's ok
1917 The value assigned to a constant expression must be known at compile time,
1918 which is not the case when dereferencing raw pointers. Erroneous code
1922 const foo: i32 = 42;
1923 const baz: *const i32 = (&foo as *const i32);
1925 const deref: i32 = *baz;
1926 // error: raw pointers cannot be dereferenced in constants
1929 To fix this error, please do not assign this value to a constant expression.
1933 const foo: i32 = 42;
1934 const baz: *const i32 = (&foo as *const i32);
1936 unsafe { let deref: i32 = *baz; }
1937 // baz isn't a constant expression so it's ok
1940 You'll also note that this assignment must be done in an unsafe block!
1944 It is not allowed for a mutable static to allocate or have destructors. For
1948 // error: mutable statics are not allowed to have boxes
1949 static mut FOO: Option<Box<usize>> = None;
1951 // error: mutable statics are not allowed to have destructors
1952 static mut BAR: Option<Vec<i32>> = None;
1957 In Rust 1.3, the default object lifetime bounds are expected to
1958 change, as described in RFC #1156 [1]. You are getting a warning
1959 because the compiler thinks it is possible that this change will cause
1960 a compilation error in your code. It is possible, though unlikely,
1961 that this is a false alarm.
1963 The heart of the change is that where `&'a Box<SomeTrait>` used to
1964 default to `&'a Box<SomeTrait+'a>`, it now defaults to `&'a
1965 Box<SomeTrait+'static>` (here, `SomeTrait` is the name of some trait
1966 type). Note that the only types which are affected are references to
1967 boxes, like `&Box<SomeTrait>` or `&[Box<SomeTrait>]`. More common
1968 types like `&SomeTrait` or `Box<SomeTrait>` are unaffected.
1970 To silence this warning, edit your code to use an explicit bound.
1971 Most of the time, this means that you will want to change the
1972 signature of a function that you are calling. For example, if
1973 the error is reported on a call like `foo(x)`, and `foo` is
1977 fn foo(arg: &Box<SomeTrait>) { ... }
1980 you might change it to:
1983 fn foo<'a>(arg: &Box<SomeTrait+'a>) { ... }
1986 This explicitly states that you expect the trait object `SomeTrait` to
1987 contain references (with a maximum lifetime of `'a`).
1989 [1]: https://github.com/rust-lang/rfcs/pull/1156
1993 A user-defined dereference was attempted in an invalid context. Erroneous
1997 use std::ops::Deref;
2004 fn deref(&self)-> &str { "foo" }
2007 const S: &'static str = &A;
2008 // error: user-defined dereference operators are not allowed in constants
2015 You cannot directly use a dereference operation whilst initializing a constant
2016 or a static. To fix this error, restructure your code to avoid this dereference,
2017 perhaps moving it inline:
2020 use std::ops::Deref;
2027 fn deref(&self)-> &str { "foo" }
2031 let foo : &str = &A;
2037 An invalid lint attribute has been given. Erroneous code example:
2040 #![allow(foo = "")] // error: malformed lint attribute
2043 Lint attributes only accept a list of identifiers (where each identifier is a
2044 lint name). Ensure the attribute is of this form:
2047 #![allow(foo)] // ok!
2049 #![allow(foo, foo2)] // ok!
2054 A borrow of a constant containing interior mutability was attempted. Erroneous
2058 use std::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT};
2060 const A: AtomicUsize = ATOMIC_USIZE_INIT;
2061 static B: &'static AtomicUsize = &A;
2062 // error: cannot borrow a constant which contains interior mutability, create a
2066 A `const` represents a constant value that should never change. If one takes
2067 a `&` reference to the constant, then one is taking a pointer to some memory
2068 location containing the value. Normally this is perfectly fine: most values
2069 can't be changed via a shared `&` pointer, but interior mutability would allow
2070 it. That is, a constant value could be mutated. On the other hand, a `static` is
2071 explicitly a single memory location, which can be mutated at will.
2073 So, in order to solve this error, either use statics which are `Sync`:
2076 use std::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT};
2078 static A: AtomicUsize = ATOMIC_USIZE_INIT;
2079 static B: &'static AtomicUsize = &A; // ok!
2082 You can also have this error while using a cell type:
2085 #![feature(const_fn)]
2087 use std::cell::Cell;
2089 const A: Cell<usize> = Cell::new(1);
2090 const B: &'static Cell<usize> = &A;
2091 // error: cannot borrow a constant which contains interior mutability, create
2095 struct C { a: Cell<usize> }
2097 const D: C = C { a: Cell::new(1) };
2098 const E: &'static Cell<usize> = &D.a; // error
2101 const F: &'static C = &D; // error
2104 This is because cell types do operations that are not thread-safe. Due to this,
2105 they don't implement Sync and thus can't be placed in statics. In this
2106 case, `StaticMutex` would work just fine, but it isn't stable yet:
2107 https://doc.rust-lang.org/nightly/std/sync/struct.StaticMutex.html
2109 However, if you still wish to use these types, you can achieve this by an unsafe
2113 #![feature(const_fn)]
2115 use std::cell::Cell;
2116 use std::marker::Sync;
2118 struct NotThreadSafe<T> {
2122 unsafe impl<T> Sync for NotThreadSafe<T> {}
2124 static A: NotThreadSafe<usize> = NotThreadSafe { value : Cell::new(1) };
2125 static B: &'static NotThreadSafe<usize> = &A; // ok!
2128 Remember this solution is unsafe! You will have to ensure that accesses to the
2129 cell are synchronized.
2133 A type with a destructor was assigned to an invalid type of variable. Erroneous
2142 fn drop(&mut self) {}
2145 const F : Foo = Foo { a : 0 };
2146 // error: constants are not allowed to have destructors
2147 static S : Foo = Foo { a : 0 };
2148 // error: statics are not allowed to have destructors
2151 To solve this issue, please use a type which does allow the usage of type with
2156 A reference of an interior static was assigned to another const/static.
2157 Erroneous code example:
2164 static S : Foo = Foo { a : 0 };
2165 static A : &'static u32 = &S.a;
2166 // error: cannot refer to the interior of another static, use a
2170 The "base" variable has to be a const if you want another static/const variable
2171 to refer to one of its fields. Example:
2178 const S : Foo = Foo { a : 0 };
2179 static A : &'static u32 = &S.a; // ok!
2184 A lifetime name is shadowing another lifetime name. Erroneous code example:
2192 fn f<'a>(x: &'a i32) { // error: lifetime name `'a` shadows a lifetime
2193 // name that is already in scope
2198 Please change the name of one of the lifetimes to remove this error. Example:
2206 fn f<'b>(x: &'b i32) { // ok!
2216 A stability attribute was used outside of the standard library. Erroneous code
2220 #[stable] // error: stability attributes may not be used outside of the
2225 It is not possible to use stability attributes outside of the standard library.
2226 Also, for now, it is not possible to write deprecation messages either.
2230 This error indicates that a `#[repr(..)]` attribute was placed on an unsupported
2233 Examples of erroneous code:
2243 struct Foo {bar: bool, baz: bool}
2251 - The `#[repr(C)]` attribute can only be placed on structs and enums
2252 - The `#[repr(packed)]` and `#[repr(simd)]` attributes only work on structs
2253 - The `#[repr(u8)]`, `#[repr(i16)]`, etc attributes only work on enums
2255 These attributes do not work on typedefs, since typedefs are just aliases.
2257 Representations like `#[repr(u8)]`, `#[repr(i64)]` are for selecting the
2258 discriminant size for C-like enums (when there is no associated data, e.g. `enum
2259 Color {Red, Blue, Green}`), effectively setting the size of the enum to the size
2260 of the provided type. Such an enum can be cast to a value of the same type as
2261 well. In short, `#[repr(u8)]` makes the enum behave like an integer with a
2262 constrained set of allowed values.
2264 Only C-like enums can be cast to numerical primitives, so this attribute will
2265 not apply to structs.
2267 `#[repr(packed)]` reduces padding to make the struct size smaller. The
2268 representation of enums isn't strictly defined in Rust, and this attribute won't
2271 `#[repr(simd)]` will give a struct consisting of a homogenous series of machine
2272 types (i.e. `u8`, `i32`, etc) a representation that permits vectorization via
2273 SIMD. This doesn't make much sense for enums since they don't consist of a
2274 single list of data.
2278 This error indicates that an `#[inline(..)]` attribute was incorrectly placed on
2279 something other than a function or method.
2281 Examples of erroneous code:
2293 `#[inline]` hints the compiler whether or not to attempt to inline a method or
2294 function. By default, the compiler does a pretty good job of figuring this out
2295 itself, but if you feel the need for annotations, `#[inline(always)]` and
2296 `#[inline(never)]` can override or force the compiler's decision.
2298 If you wish to apply this attribute to all methods in an impl, manually annotate
2299 each method; it is not possible to annotate the entire impl with an `#[inline]`
2306 register_diagnostics! {
2307 // E0006 // merged with E0005
2310 E0278, // requirement is not satisfied
2311 E0279, // requirement is not satisfied
2312 E0280, // requirement is not satisfied
2313 E0284, // cannot resolve type
2314 E0285, // overflow evaluation builtin bounds
2315 E0298, // mismatched types between arms
2316 E0299, // mismatched types between arms
2317 // E0300, // unexpanded macro
2318 // E0304, // expected signed integer constant
2319 // E0305, // expected constant
2320 E0311, // thing may not live long enough
2321 E0312, // lifetime of reference outlives lifetime of borrowed content
2322 E0313, // lifetime of borrowed pointer outlives lifetime of captured variable
2323 E0314, // closure outlives stack frame
2324 E0315, // cannot invoke closure outside of its lifetime
2325 E0316, // nested quantification of lifetimes
2326 E0453, // overruled by outer forbid
2327 E0471, // constant evaluation error: ..
2328 E0473, // dereference of reference outside its lifetime
2329 E0474, // captured variable `..` does not outlive the enclosing closure
2330 E0475, // index of slice outside its lifetime
2331 E0476, // lifetime of the source pointer does not outlive lifetime bound...
2332 E0477, // the type `..` does not fulfill the required lifetime...
2333 E0478, // lifetime bound not satisfied
2334 E0479, // the type `..` (provided as the value of a type parameter) is...
2335 E0480, // lifetime of method receiver does not outlive the method call
2336 E0481, // lifetime of function argument does not outlive the function call
2337 E0482, // lifetime of return value does not outlive the function call
2338 E0483, // lifetime of operand does not outlive the operation
2339 E0484, // reference is not valid at the time of borrow
2340 E0485, // automatically reference is not valid at the time of borrow
2341 E0486, // type of expression contains references that are not valid during...
2342 E0487, // unsafe use of destructor: destructor might be called while...
2343 E0488, // lifetime of variable does not enclose its declaration
2344 E0489, // type/lifetime parameter not in scope here
2345 E0490, // a value of type `..` is borrowed for too long
2346 E0491, // in type `..`, reference has a longer lifetime than the data it...
2347 E0495, // cannot infer an appropriate lifetime due to conflicting requirements