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Diffstat (limited to '')
-rw-r--r-- | library/alloc/src/vec/is_zero.rs | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/library/alloc/src/vec/is_zero.rs b/library/alloc/src/vec/is_zero.rs index 2e025c8a4..8e652d676 100644 --- a/library/alloc/src/vec/is_zero.rs +++ b/library/alloc/src/vec/is_zero.rs @@ -160,3 +160,25 @@ unsafe impl<T: IsZero> IsZero for Saturating<T> { self.0.is_zero() } } + +macro_rules! impl_for_optional_bool { + ($($t:ty,)+) => {$( + unsafe impl IsZero for $t { + #[inline] + fn is_zero(&self) -> bool { + // SAFETY: This is *not* a stable layout guarantee, but + // inside `core` we're allowed to rely on the current rustc + // behaviour that options of bools will be one byte with + // no padding, so long as they're nested less than 254 deep. + let raw: u8 = unsafe { core::mem::transmute(*self) }; + raw == 0 + } + } + )+}; +} +impl_for_optional_bool! { + Option<bool>, + Option<Option<bool>>, + Option<Option<Option<bool>>>, + // Could go further, but not worth the metadata overhead +} |