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Remove explicit-generic-args-with-impl-trait docs from unstable book

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Signed-off-by: Nick Cameron <nrc@ncameron.org>
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Nick Cameron 2022-05-09 12:27:54 +01:00
parent 6609c6734d
commit 12872b6807
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src/doc/unstable-book/src/language-features/explicit-generic-args-with-impl-trait.md
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# `explicit_generic_args_with_impl_trait`
The tracking issue for this feature is: [#83701]
[#83701]: https://github.com/rust-lang/rust/issues/83701
------------------------
The `explicit_generic_args_with_impl_trait` feature gate lets you specify generic arguments even
when `impl Trait` is used in argument position.
A simple example is:
```rust
#![feature(explicit_generic_args_with_impl_trait)]
fn foo<T: ?Sized>(_f: impl AsRef<T>) {}
fn main() {
foo::<str>("".to_string());
}
```
This is currently rejected:
```text
error[E0632]: cannot provide explicit generic arguments when `impl Trait` is used in argument position
--> src/main.rs:6:11
|
6 | foo::<str>("".to_string());
| ^^^ explicit generic argument not allowed
```
However it would compile if `explicit_generic_args_with_impl_trait` is enabled.
Note that the synthetic type parameters from `impl Trait` are still implicit and you
cannot explicitly specify these:
```rust,compile_fail
#![feature(explicit_generic_args_with_impl_trait)]
fn foo<T: ?Sized>(_f: impl AsRef<T>) {}
fn bar<T: ?Sized, F: AsRef<T>>(_f: F) {}
fn main() {
bar::<str, _>("".to_string()); // Okay
bar::<str, String>("".to_string()); // Okay
foo::<str>("".to_string()); // Okay
foo::<str, String>("".to_string()); // Error, you cannot specify `impl Trait` explicitly
}
```