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make mem::Discriminant invariant #71814

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make mem::Discriminant invariant #71814

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3 changes: 2 additions & 1 deletion src/libcore/mem/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -929,8 +929,9 @@ pub unsafe fn transmute_copy<T, U>(src: &T) -> U {
/// See the [`discriminant`] function in this module for more information.
///
/// [`discriminant`]: fn.discriminant.html
// We use `PhantomData<fn(T) -> T>` because we want `Discriminant` to be invariant.
#[stable(feature = "discriminant_value", since = "1.21.0")]
pub struct Discriminant<T>(u64, PhantomData<fn() -> T>);
pub struct Discriminant<T>(u64, PhantomData<fn(T) -> T>);

// N.B. These trait implementations cannot be derived because we don't want any bounds on T.

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