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| -rw-r--r-- | library/core/src/mem/mod.rs | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs index 732fcce0f29..bc701d97bbb 100644 --- a/library/core/src/mem/mod.rs +++ b/library/core/src/mem/mod.rs @@ -1126,6 +1126,11 @@ impl<T> fmt::Debug for Discriminant<T> { /// /// [Reference]: ../../reference/items/enumerations.html#custom-discriminant-values-for-fieldless-enumerations /// +/// The value of a [`Discriminant<T>`] is independent of any *lifetimes* in `T`. As such, reading +/// or writing a `Discriminant<Foo<'a>>` as a `Discriminant<Foo<'b>>` (whether via [`transmute`] or +/// otherwise) is always sound. Note that this is **not** true for other kinds of generic +/// parameters; `Discriminant<Foo<A>>` and `Discriminant<Foo<B>>` might be incompatible. +/// /// # Examples /// /// This can be used to compare enums that carry data, while disregarding |