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Document PointerLike implementation restrictions. #134602

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Dec 22, 2024
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Document PointerLike implementation restrictions. #134602

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10 changes: 8 additions & 2 deletions library/core/src/marker.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -982,8 +982,14 @@ pub trait Tuple {}

/// A marker for pointer-like types.
///
/// This trait can only be implemented for types that have the same size and alignment
/// as a `usize` or `*const ()`.
/// This trait can only be implemented for types that are certain to have
/// the same size and alignment as a [`usize`] or [`*const ()`](pointer).
/// To ensure this, there are special requirements on implementations
/// of `PointerLike` (other than the already-provided implementations
/// for built-in types):
///
/// * The type must have `#[repr(transparent)]`.
/// * The type’s sole non-zero-sized field must itself implement `PointerLike`.
#[unstable(feature = "pointer_like_trait", issue = "none")]
#[lang = "pointer_like"]
#[diagnostic::on_unimplemented(
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