::never-say-never
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::Infallibleis a sad instance of the latter.
That is, the following fails to compile:
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!
use ::never_say_never::Never;
let x: u32 = match Ok::<_, Never>(42) {
| Ok(it) => it,
| Err(unreachable) => unreachable,
};
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