never-say-never.rs

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never-say-never.rs

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The never type (the true one!) in stable Rust.

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# `::never-say-never`

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The `!` type. In stable Rust. Since `1.14.0`.

Better than an `enum Never {}` definition would be, since an instance of
type `!` automagically coerces to any type, whereas an instance of
`enum EmptyEnum {}` needs an explicit `match it {}`.

- Currently, [`::core::convert::Infallible`] is a sad instance of the
    latter.

[`::core::convert::Infallible`]: https://doc.rust-lang.org/1.58.0/core/convert/enum.Infallible.html

That is, the following fails to compile:

```rust ,compile_fail
let x: u32 = match <u32 as TryFrom<u8>>::try_from(42) {
    | Ok(it) => it,
    | Err(unreachable) => unreachable, // Error, expected `u32`, found `Infallible`
};
```

but the following doesn't!

```rust
use ::never_say_never::Never;

let x: u32 = match Ok::<_, Never>(42) {
    | Ok(it) => it,
    | Err(unreachable) => unreachable,
};
```

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