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//! Helper module for exporting the `pattern_type` macro
/// Creates a pattern type.
/// ```ignore (cannot test this from within core yet)
/// type Positive = std::pat::pattern_type!(i32 is 1..);
/// ```
#[macro_export]
#[rustc_builtin_macro(pattern_type)]
#[unstable(feature = "pattern_type_macro", issue = "123646")]
macro_rules! pattern_type {
($($arg:tt)*) => {
/* compiler built-in */
};
}
/// A trait implemented for integer types and `char`.
/// Useful in the future for generic pattern types, but
/// used right now to simplify ast lowering of pattern type ranges.
#[unstable(feature = "pattern_type_range_trait", issue = "123646")]
#[rustc_const_unstable(feature = "pattern_type_range_trait", issue = "123646")]
#[const_trait]
#[diagnostic::on_unimplemented(
message = "`{Self}` is not a valid base type for range patterns",
label = "only integer types and `char` are supported"
)]
pub trait RangePattern {
/// Trait version of the inherent `MIN` assoc const.
#[cfg_attr(not(bootstrap), lang = "RangeMin")]
const MIN: Self;
/// Trait version of the inherent `MIN` assoc const.
#[cfg_attr(not(bootstrap), lang = "RangeMax")]
const MAX: Self;
/// A compile-time helper to subtract 1 for exclusive ranges.
#[cfg_attr(not(bootstrap), lang = "RangeSub")]
#[track_caller]
fn sub_one(self) -> Self;
}
macro_rules! impl_range_pat {
($($ty:ty,)*) => {
$(
#[rustc_const_unstable(feature = "pattern_type_range_trait", issue = "123646")]
impl const RangePattern for $ty {
const MIN: $ty = <$ty>::MIN;
const MAX: $ty = <$ty>::MAX;
fn sub_one(self) -> Self {
match self.checked_sub(1) {
Some(val) => val,
None => panic!("exclusive range end at minimum value of type")
}
}
}
)*
}
}
impl_range_pat! {
i8, i16, i32, i64, i128, isize,
u8, u16, u32, u64, u128, usize,
}
#[rustc_const_unstable(feature = "pattern_type_range_trait", issue = "123646")]
impl const RangePattern for char {
const MIN: Self = char::MIN;
const MAX: Self = char::MAX;
fn sub_one(self) -> Self {
match char::from_u32(self as u32 - 1) {
None => panic!("exclusive range to start of valid chars"),
Some(val) => val,
}
}
}
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