--- /dev/null
+# `tuple_struct_self_ctor`
+
+The tracking issue for this feature is: [#51994]
+[#51994]: https://github.com/rust-lang/rust/issues/51994
+
+------------------------
+
+The `tuple_struct_self_ctor` feature gate lets you use the special `Self`
+identifier as a constructor and a pattern.
+
+A simple example is:
+
+```rust
+#![feature(tuple_struct_self_ctor)]
+
+struct ST(i32, i32);
+
+impl ST {
+ fn new() -> Self {
+ ST(0, 1)
+ }
+
+ fn ctor() -> Self {
+ Self(1,2) // constructed by `Self`, it is the same as `ST(1, 2)`
+ }
+
+ fn pattern(self) {
+ match self {
+ Self(x, y) => println!("{} {}", x, y), // used as a pattern
+ }
+ }
+}
+```
CtorKind::from_ast(struct_def));
self.define(parent, ident, ValueNS, (ctor_def, ctor_vis, sp, expansion));
self.struct_constructors.insert(def.def_id(), (ctor_def, ctor_vis));
+ self.tuple_structs.insert(def.def_id(), ctor_def);
}
}
self.cstore.def_key(def_id).parent
.map(|index| DefId { krate: def_id.krate, index: index }) {
self.struct_constructors.insert(struct_def_id, (def, vis));
+ self.tuple_structs.insert(struct_def_id, def);
}
}
Def::Trait(..) => {
/// it's not used during normal resolution, only for better error reporting.
struct_constructors: DefIdMap<(Def, ty::Visibility)>,
+ /// Map from tuple struct's DefId to VariantData's Def
+ tuple_structs: DefIdMap<Def>,
+
/// Only used for better errors on `fn(): fn()`
current_type_ascription: Vec<Span>,
warned_proc_macros: FxHashSet(),
potentially_unused_imports: Vec::new(),
struct_constructors: DefIdMap(),
+ tuple_structs: DefIdMap(),
found_unresolved_macro: false,
unused_macros: FxHashSet(),
current_type_ascription: Vec::new(),
None
}
+ fn resolve_adt(&mut self, item: &Item, generics: &Generics) {
+ self.with_type_parameter_rib(HasTypeParameters(generics, ItemRibKind), |this| {
+ let item_def_id = this.definitions.local_def_id(item.id);
+ if this.session.features_untracked().self_in_typedefs {
+ this.with_self_rib(Def::SelfTy(None, Some(item_def_id)), |this| {
+ visit::walk_item(this, item);
+ });
+ } else {
+ visit::walk_item(this, item);
+ }
+ });
+ }
+
fn resolve_item(&mut self, item: &Item) {
let name = item.ident.name;
debug!("(resolving item) resolving {}", name);
|this| visit::walk_item(this, item));
}
+ ItemKind::Struct(ref variant, ref generics) => {
+ if variant.is_tuple() || variant.is_unit() {
+ if let Some(def_id) = self.definitions.opt_local_def_id(item.id) {
+ if let Some(variant_id) = self.definitions.opt_local_def_id(variant.id()) {
+ let variant_def = if variant.is_tuple() {
+ Def::StructCtor(variant_id, CtorKind::Fn)
+ } else {
+ Def::StructCtor(variant_id, CtorKind::Const)
+ };
+ self.tuple_structs.insert(def_id, variant_def);
+ }
+ }
+ }
+ self.resolve_adt(item, generics);
+ }
+
ItemKind::Enum(_, ref generics) |
- ItemKind::Struct(_, ref generics) |
ItemKind::Union(_, ref generics) => {
- self.with_type_parameter_rib(HasTypeParameters(generics, ItemRibKind), |this| {
- let item_def_id = this.definitions.local_def_id(item.id);
- if this.session.features_untracked().self_in_typedefs {
- this.with_self_rib(Def::SelfTy(None, Some(item_def_id)), |this| {
- visit::walk_item(this, item);
- });
- } else {
- visit::walk_item(this, item);
- }
- });
+ self.resolve_adt(item, generics);
}
ItemKind::Impl(.., ref generics, ref opt_trait_ref, ref self_type, ref impl_items) =>
self.ribs[TypeNS].pop();
}
+ fn with_tuple_struct_self_ctor_rib<F>(&mut self, self_ty: &Ty, f: F)
+ where F: FnOnce(&mut Resolver)
+ {
+ let variant_def = if self.session.features_untracked().tuple_struct_self_ctor {
+ let base_def = self.def_map.get(&self_ty.id).map(|r| r.base_def());
+ if let Some(Def::Struct(ref def_id)) = base_def {
+ self.tuple_structs.get(def_id).cloned()
+ } else {
+ None
+ }
+ } else {
+ None
+ };
+
+ // when feature gate is enabled and `Self` is a tuple struct
+ if let Some(variant_def) = variant_def {
+ let mut self_type_rib = Rib::new(NormalRibKind);
+ self_type_rib.bindings.insert(keywords::SelfType.ident(), variant_def);
+ self.ribs[ValueNS].push(self_type_rib);
+ f(self);
+ self.ribs[ValueNS].pop();
+ } else {
+ f(self);
+ }
+ }
+
fn resolve_implementation(&mut self,
generics: &Generics,
opt_trait_reference: &Option<TraitRef>,
ValueNS,
impl_item.span,
|n, s| MethodNotMemberOfTrait(n, s));
-
- visit::walk_impl_item(this, impl_item);
+ this.with_tuple_struct_self_ctor_rib(self_type, |this| {
+ visit::walk_impl_item(this, impl_item);
+ });
}
ImplItemKind::Type(ref ty) => {
// If this is a trait impl, ensure the type
// Non-builtin attributes in inner attribute position
(active, custom_inner_attributes, "1.30.0", Some(38356), None),
+
+ // tuple struct self constructor (RFC 2302)
+ (active, tuple_struct_self_ctor, "1.31.0", Some(51994), None),
);
declare_features! (
ast::ExprKind::Async(..) => {
gate_feature_post!(&self, async_await, e.span, "async blocks are unstable");
}
+ ast::ExprKind::Call(ref callee, _) => {
+ if let ast::ExprKind::Path(_, ref p) = callee.node {
+ if p.segments.len() == 1 &&
+ p.segments[0].ident.name == keywords::SelfType.name() {
+ gate_feature_post!(&self, tuple_struct_self_ctor, e.span,
+ "tuple struct Self constructors are unstable");
+ }
+ }
+ }
_ => {}
}
visit::walk_expr(self, e);
--- /dev/null
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(tuple_struct_self_ctor)]
+
+#![allow(dead_code)]
+
+use std::fmt::Display;
+
+struct ST1(i32, i32);
+
+impl ST1 {
+ fn new() -> Self {
+ ST1(0, 1)
+ }
+
+ fn ctor() -> Self {
+ Self(1,2) // Self as a constructor
+ }
+
+ fn pattern(self) {
+ match self {
+ Self(x, y) => println!("{} {}", x, y), // Self as a pattern
+ }
+ }
+}
+
+struct ST2<T>(T); // With type parameter
+
+impl<T> ST2<T> where T: Display {
+
+ fn ctor(v: T) -> Self {
+ Self(v)
+ }
+
+ fn pattern(&self) {
+ match self {
+ Self(ref v) => println!("{}", v),
+ }
+ }
+}
+
+struct ST3<'a>(&'a i32); // With lifetime parameter
+
+impl<'a> ST3<'a> {
+
+ fn ctor(v: &'a i32) -> Self {
+ Self(v)
+ }
+
+ fn pattern(self) {
+ let Self(ref v) = self;
+ println!("{}", v);
+ }
+}
+
+struct ST4(usize);
+
+impl ST4 {
+ fn map(opt: Option<usize>) -> Option<Self> {
+ opt.map(Self) // use `Self` as a function passed somewhere
+ }
+}
+
+struct ST5; // unit struct
+
+impl ST5 {
+ fn ctor() -> Self {
+ Self // `Self` as a unit struct value
+ }
+
+ fn pattern(self) -> Self {
+ match self {
+ Self => Self, // `Self` as a unit struct value for matching
+ }
+ }
+}
+
+fn main() {
+ let v1 = ST1::ctor();
+ v1.pattern();
+
+ let v2 = ST2::ctor(10);
+ v2.pattern();
+
+ let local = 42;
+ let v3 = ST3::ctor(&local);
+ v3.pattern();
+
+ let v4 = Some(1usize);
+ let _ = ST4::map(v4);
+
+ let v5 = ST5::ctor();
+ v5.pattern();
+}
--- /dev/null
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct ST(i32, i32);
+
+impl ST {
+ fn ctor() -> Self {
+ Self(1,2)
+ //~^ ERROR: expected function, found self type `Self` [E0423]
+ //~^^ ERROR: tuple struct Self constructors are unstable (see issue #51994) [E0658]
+ }
+}
--- /dev/null
+error[E0423]: expected function, found self type `Self`
+ --> $DIR/feature-gate-tuple-struct-self-ctor.rs:15:9
+ |
+LL | Self(1,2)
+ | ^^^^ not a function
+ |
+ = note: can't use `Self` as a constructor, you must use the implemented struct
+
+error[E0658]: tuple struct Self constructors are unstable (see issue #51994)
+ --> $DIR/feature-gate-tuple-struct-self-ctor.rs:15:9
+ |
+LL | Self(1,2)
+ | ^^^^^^^^^
+ |
+ = help: add #![feature(tuple_struct_self_ctor)] to the crate attributes to enable
+
+error: aborting due to 2 previous errors
+
+Some errors occurred: E0423, E0658.
+For more information about an error, try `rustc --explain E0423`.
struct S(u8, u16);
type A = S;
-impl S {
- fn f() {
- let s = Self(0, 1); //~ ERROR expected function
- match s {
- Self(..) => {} //~ ERROR expected tuple struct/variant
- }
- }
-}
-
fn main() {
let s = A(0, 1); //~ ERROR expected function
match s {
-error[E0423]: expected function, found self type `Self`
- --> $DIR/tuple-struct-alias.rs:16:17
- |
-LL | let s = Self(0, 1); //~ ERROR expected function
- | ^^^^ not a function
- |
- = note: can't use `Self` as a constructor, you must use the implemented struct
-
-error[E0532]: expected tuple struct/variant, found self type `Self`
- --> $DIR/tuple-struct-alias.rs:18:13
- |
-LL | Self(..) => {} //~ ERROR expected tuple struct/variant
- | ^^^^ not a tuple struct/variant
- |
- = note: can't use `Self` as a constructor, you must use the implemented struct
-
error[E0423]: expected function, found type alias `A`
- --> $DIR/tuple-struct-alias.rs:24:13
+ --> $DIR/tuple-struct-alias.rs:15:13
|
LL | let s = A(0, 1); //~ ERROR expected function
| ^ did you mean `S`?
= note: can't use a type alias as a constructor
error[E0532]: expected tuple struct/variant, found type alias `A`
- --> $DIR/tuple-struct-alias.rs:26:9
+ --> $DIR/tuple-struct-alias.rs:17:9
|
LL | A(..) => {} //~ ERROR expected tuple struct/variant
| ^ did you mean `S`?
|
= note: can't use a type alias as a constructor
-error: aborting due to 4 previous errors
+error: aborting due to 2 previous errors
Some errors occurred: E0423, E0532.
For more information about an error, try `rustc --explain E0423`.
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