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Rollup merge of #89885 - cameron1024:long-explanation-E0183, r=GuillaumeGomez

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add long explanation for E0183

Addresses #61137
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Matthias Krüger 2021-10-15 07:44:49 +02:00 • committed by GitHub
commit e3099e7d8c
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2
compiler/rustc_error_codes/src/error_codes.rs
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@ -92,6 +92,7 @@ E0164: include_str!("./error_codes/E0164.md"),
E0165: include_str!("./error_codes/E0165.md"),
E0170: include_str!("./error_codes/E0170.md"),
E0178: include_str!("./error_codes/E0178.md"),
E0183: include_str!("./error_codes/E0183.md"),
E0184: include_str!("./error_codes/E0184.md"),
E0185: include_str!("./error_codes/E0185.md"),
E0186: include_str!("./error_codes/E0186.md"),
@ -513,7 +514,6 @@ E0785: include_str!("./error_codes/E0785.md"),
// E0173, // manual implementations of unboxed closure traits are experimental
// E0174,
// E0182, // merged into E0229
E0183,
// E0187, // cannot infer the kind of the closure
// E0188, // can not cast an immutable reference to a mutable pointer
// E0189, // deprecated: can only cast a boxed pointer to a boxed object

39
compiler/rustc_error_codes/src/error_codes/E0183.md Normal file
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@ -0,0 +1,39 @@
Manual implemetation of a `Fn*` trait.
Erroneous code example:
```compile_fail,E0183
struct MyClosure {
foo: i32
}
impl FnOnce<()> for MyClosure { // error
type Output = ();
extern "rust-call" fn call_once(self, args: ()) -> Self::Output {
println!("{}", self.foo);
}
}
```
Manually implementing `Fn`, `FnMut` or `FnOnce` is unstable
and requires `#![feature(fn_traits, unboxed_closures)]`.
```
#![feature(fn_traits, unboxed_closures)]
struct MyClosure {
foo: i32
}
impl FnOnce<()> for MyClosure { // ok!
type Output = ();
extern "rust-call" fn call_once(self, args: ()) -> Self::Output {
println!("{}", self.foo);
}
}
```
The argumements must be a tuple representing the argument list.
For more info, see the [tracking issue][iss29625]:
[iss29625]: https://github.com/rust-lang/rust/issues/29625