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Diffstat (limited to 'library/core/src/mem/transmutability.rs')
-rw-r--r-- | library/core/src/mem/transmutability.rs | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/library/core/src/mem/transmutability.rs b/library/core/src/mem/transmutability.rs new file mode 100644 index 000000000..b59a5b89d --- /dev/null +++ b/library/core/src/mem/transmutability.rs @@ -0,0 +1,43 @@ +/// Are values of a type transmutable into values of another type? +/// +/// This trait is implemented on-the-fly by the compiler for types `Src` and `Self` when the bits of +/// any value of type `Self` are safely transmutable into a value of type `Dst`, in a given `Context`, +/// notwithstanding whatever safety checks you have asked the compiler to [`Assume`] are satisfied. +#[unstable(feature = "transmutability", issue = "99571")] +#[cfg_attr(not(bootstrap), lang = "transmute_trait")] +#[rustc_on_unimplemented( + message = "`{Src}` cannot be safely transmuted into `{Self}` in the defining scope of `{Context}`.", + label = "`{Src}` cannot be safely transmuted into `{Self}` in the defining scope of `{Context}`." +)] +pub unsafe trait BikeshedIntrinsicFrom< + Src, + Context, + const ASSUME_ALIGNMENT: bool, + const ASSUME_LIFETIMES: bool, + const ASSUME_VALIDITY: bool, + const ASSUME_VISIBILITY: bool, +> where + Src: ?Sized, +{ +} + +/// What transmutation safety conditions shall the compiler assume that *you* are checking? +#[unstable(feature = "transmutability", issue = "99571")] +#[derive(PartialEq, Eq, Clone, Copy, Debug)] +pub struct Assume { + /// When `true`, the compiler assumes that *you* are ensuring (either dynamically or statically) that + /// destination referents do not have stricter alignment requirements than source referents. + pub alignment: bool, + + /// When `true`, the compiler assume that *you* are ensuring that lifetimes are not extended in a manner + /// that violates Rust's memory model. + pub lifetimes: bool, + + /// When `true`, the compiler assumes that *you* are ensuring that the source type is actually a valid + /// instance of the destination type. + pub validity: bool, + + /// When `true`, the compiler assumes that *you* have ensured that it is safe for you to violate the + /// type and field privacy of the destination type (and sometimes of the source type, too). + pub visibility: bool, +} |