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Make phantom variance markers transparent #137054

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Mar 4, 2025
+12 −0
Merged

Make phantom variance markers transparent #137054

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12 changes: 12 additions & 0 deletions library/core/src/marker/variance.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,8 @@ phantom_lifetime! {
/// For all `'a`, the following are guaranteed:
/// * `size_of::<PhantomCovariantLifetime<'a>>() == 0`
/// * `align_of::<PhantomCovariantLifetime<'a>>() == 1`
#[rustc_pub_transparent]
#[repr(transparent)]
pub struct PhantomCovariantLifetime<'a>(PhantomCovariant<&'a ()>);
/// Zero-sized type used to mark a lifetime as contravariant.
///
Expand All @@ -149,6 +151,8 @@ phantom_lifetime! {
/// For all `'a`, the following are guaranteed:
/// * `size_of::<PhantomContravariantLifetime<'a>>() == 0`
/// * `align_of::<PhantomContravariantLifetime<'a>>() == 1`
#[rustc_pub_transparent]
#[repr(transparent)]
pub struct PhantomContravariantLifetime<'a>(PhantomContravariant<&'a ()>);
/// Zero-sized type used to mark a lifetime as invariant.
///
Expand All @@ -162,6 +166,8 @@ phantom_lifetime! {
/// For all `'a`, the following are guaranteed:
/// * `size_of::<PhantomInvariantLifetime<'a>>() == 0`
/// * `align_of::<PhantomInvariantLifetime<'a>>() == 1`
#[rustc_pub_transparent]
#[repr(transparent)]
pub struct PhantomInvariantLifetime<'a>(PhantomInvariant<&'a ()>);
}

Expand All @@ -179,6 +185,8 @@ phantom_type! {
/// For all `T`, the following are guaranteed:
/// * `size_of::<PhantomCovariant<T>>() == 0`
/// * `align_of::<PhantomCovariant<T>>() == 1`
#[rustc_pub_transparent]
#[repr(transparent)]
pub struct PhantomCovariant<T>(PhantomData<fn() -> T>);
/// Zero-sized type used to mark a type parameter as contravariant.
///
Expand All @@ -193,6 +201,8 @@ phantom_type! {
/// For all `T`, the following are guaranteed:
/// * `size_of::<PhantomContravariant<T>>() == 0`
/// * `align_of::<PhantomContravariant<T>>() == 1`
#[rustc_pub_transparent]
#[repr(transparent)]
pub struct PhantomContravariant<T>(PhantomData<fn(T)>);
/// Zero-sized type used to mark a type parameter as invariant.
///
Expand All @@ -206,6 +216,8 @@ phantom_type! {
/// For all `T`, the following are guaranteed:
/// * `size_of::<PhantomInvariant<T>>() == 0`
/// * `align_of::<PhantomInvariant<T>>() == 1`
#[rustc_pub_transparent]
#[repr(transparent)]
pub struct PhantomInvariant<T>(PhantomData<fn(T) -> T>);
}

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