* [modules](#modules)
* [functions](#functions)
* [type definitions](grammar.html#type-definitions)
-* [structures](#structures)
+* [structs](#structs)
* [enumerations](#enumerations)
* [constant items](#constant-items)
* [static items](#static-items)
### Functions
-A _function item_ defines a sequence of [statements](#statements) and an
-optional final [expression](#expressions), along with a name and a set of
-parameters. Functions are declared with the keyword `fn`. Functions declare a
+A _function item_ defines a sequence of [statements](#statements) and a
+final [expression](#expressions), along with a name and a set of
+parameters. Other than a name, all these are optional.
+Functions are declared with the keyword `fn`. Functions may declare a
set of *input* [*variables*](#variables) as parameters, through which the caller
passes arguments into the function, and the *output* [*type*](#types)
of the value the function will return to its caller on completion.
```
fn add(x: i32, y: i32) -> i32 {
- return x + y;
+ x + y
}
```
let p: Point = (41, 68);
```
-### Structures
+### Structs
A _structure_ is a nominal [structure type](#structure-types) defined with the
keyword `struct`.
```
A _unit-like struct_ is a structure without any fields, defined by leaving off
-the list of fields entirely. Such types will have a single value. For example:
+the list of fields entirely. Such a structure implicitly defines a constant of
+its type with the same name. For example:
```
+# #![feature(braced_empty_structs)]
struct Cookie;
-let c = [Cookie, Cookie, Cookie, Cookie];
+let c = [Cookie, Cookie {}, Cookie, Cookie {}];
+```
+
+is equivalent to
+
+```
+# #![feature(braced_empty_structs)]
+struct Cookie {}
+const Cookie: Cookie = Cookie {};
+let c = [Cookie, Cookie {}, Cookie, Cookie {}];
```
The precise memory layout of a structure is not specified. One can specify a
* `target_pointer_width = "..."` - Target pointer width in bits. This is set
to `"32"` for targets with 32-bit pointers, and likewise set to `"64"` for
64-bit pointers.
+* `target_vendor = "..."` - Vendor of the target, for example `apple`, `pc`, or
+ simply `"unknown"`.
* `test` - Enabled when compiling the test harness (using the `--test` flag).
* `unix` - See `target_family`.
* `windows` - See `target_family`.
* `advanced_slice_patterns` - See the [match expressions](#match-expressions)
section for discussion; the exact semantics of
slice patterns are subject to change, so some types
- are still unstable.
+ are still unstable.
* `slice_patterns` - OK, actually, slice patterns are just scary and
completely unstable.
* `box_syntax` - Allows use of `box` expressions, the exact semantics of which
is subject to change.
+* `cfg_target_vendor` - Allows conditional compilation using the `target_vendor`
+ matcher which is subject to change.
+
* `concat_idents` - Allows use of the `concat_idents` macro, which is in many
ways insufficient for concatenating identifiers, and may be
removed entirely for something more wholesome.
terms of encapsulation).
* - `default_type_parameter_fallback` - Allows type parameter defaults to
influence type inference.
+* - `braced_empty_structs` - Allows use of empty structs with braces.
If a feature is promoted to a language feature, then all existing programs will
start to receive compilation warnings about `#![feature]` directives which enabled
### Structure expressions
There are several forms of structure expressions. A _structure expression_
-consists of the [path](#paths) of a [structure item](#structures), followed by
+consists of the [path](#paths) of a [structure item](#structs), followed by
a brace-enclosed list of one or more comma-separated name-value pairs,
providing the field values of a new instance of the structure. A field name
can be any identifier, and is separated from its value expression by a colon.
enclosing structure is mutable.
A _tuple structure expression_ consists of the [path](#paths) of a [structure
-item](#structures), followed by a parenthesized list of one or more
+item](#structs), followed by a parenthesized list of one or more
comma-separated expressions (in other words, the path of a structure item
followed by a tuple expression). The structure item must be a tuple structure
item.
A _unit-like structure expression_ consists only of the [path](#paths) of a
-[structure item](#structures).
+[structure item](#structs).
The following are examples of structure expressions:
let x = std::ops::Range {start: 0, end: 10};
let y = 0..10;
-assert_eq!(x,y);
+assert_eq!(x, y);
```
### Unary operator expressions
a lifetime preceding the loop expression, as in `'foo: loop{ }`. If a
label is present, then labeled `break` and `continue` expressions nested
within this loop may exit out of this loop or return control to its head.
-See [Break expressions](#break-expressions) and [Continue
+See [break expressions](#break-expressions) and [continue
expressions](#continue-expressions).
-### Break expressions
+### `break` expressions
A `break` expression has an optional _label_. If the label is absent, then
executing a `break` expression immediately terminates the innermost loop
present, then `break 'foo` terminates the loop with label `'foo`, which need not
be the innermost label enclosing the `break` expression, but must enclose it.
-### Continue expressions
+### `continue` expressions
A `continue` expression has an optional _label_. If the label is absent, then
executing a `continue` expression immediately terminates the current iteration
A `continue` expression is only permitted in the body of a loop.
-### While loops
+### `while` loops
A `while` loop begins by evaluating the boolean loop conditional expression.
If the loop conditional expression evaluates to `true`, the loop body block
loops](#infinite-loops), [break expressions](#break-expressions), and
[continue expressions](#continue-expressions) for more information.
-### For expressions
+### `for` expressions
A `for` expression is a syntactic construct for looping over elements provided
by an implementation of `std::iter::IntoIterator`.
-An example of a for loop over the contents of an array:
+An example of a `for` loop over the contents of an array:
```
# type Foo = i32;
loops](#infinite-loops), [break expressions](#break-expressions), and
[continue expressions](#continue-expressions) for more information.
-### If expressions
+### `if` expressions
An `if` expression is a conditional branch in program control. The form of an
`if` expression is a condition expression, followed by a consequent block, any
if` condition is evaluated. If all `if` and `else if` conditions evaluate to
`false` then any `else` block is executed.
-### Match expressions
+### `match` expressions
A `match` expression branches on a *pattern*. The exact form of matching that
occurs depends on the pattern. Patterns consist of some combination of
-literals, destructured arrays or enum constructors, structures and tuples,
+literals, destructured arrays or enum constructors, structs and tuples,
variable binding specifications, wildcards (`..`), and placeholders (`_`). A
`match` expression has a *head expression*, which is the value to compare to
the patterns. The type of the patterns must equal the type of the head
};
```
-### If let expressions
+### `if let` expressions
An `if let` expression is semantically identical to an `if` expression but in place
of a condition expression it expects a refutable let statement. If the value of the
}
```
-### While let loops
+### `while let` loops
A `while let` loop is semantically identical to a `while` loop but in place of a
condition expression it expects a refutable let statement. If the value of the
loop body block executes and control returns to the pattern matching statement.
Otherwise, the while expression completes.
-### Return expressions
+### `return` expressions
Return expressions are denoted with the keyword `return`. Evaluating a `return`
expression moves its argument into the designated output location for the
### Recursive types
Nominal types — [enumerations](#enumerated-types) and
-[structures](#structure-types) — may be recursive. That is, each `enum`
+[structs](#structure-types) — may be recursive. That is, each `enum`
constructor or `struct` field may refer, directly or indirectly, to the
enclosing `enum` or `struct` type itself. Such recursion has restrictions:
### Pointer types
All pointers in Rust are explicit first-class values. They can be copied,
-stored into data structures, and returned from functions. There are two
+stored into data structs, and returned from functions. There are two
varieties of pointer in Rust:
* References (`&`)
### Variables
A _variable_ is a component of a stack frame, either a named function parameter,
-an anonymous [temporary](#lvalues,-rvalues-and-temporaries), or a named local
+an anonymous [temporary](#lvalues-rvalues-and-temporaries), or a named local
variable.
A _local variable_ (or *stack-local* allocation) holds a value directly,
all compilation needs, and the other options are just available if more
fine-grained control is desired over the output format of a Rust crate.
-# Appendix: Rationales and design trade-offs
-
-*TODO*.
-
# Appendix: Influences
Rust is not a particularly original language, with design elements coming from
projects / rust.git / blobdiff