1 /// Are values of a type transmutable into values of another type?
3 /// This trait is implemented on-the-fly by the compiler for types `Src` and `Self` when the bits of
4 /// any value of type `Self` are safely transmutable into a value of type `Dst`, in a given `Context`,
5 /// notwithstanding whatever safety checks you have asked the compiler to [`Assume`] are satisfied.
6 #[unstable(feature = "transmutability", issue = "99571")]
7 #[cfg_attr(not(bootstrap), lang = "transmute_trait")]
8 #[rustc_on_unimplemented(
9 message = "`{Src}` cannot be safely transmuted into `{Self}` in the defining scope of `{Context}`.",
10 label = "`{Src}` cannot be safely transmuted into `{Self}` in the defining scope of `{Context}`."
12 pub unsafe trait BikeshedIntrinsicFrom<Src, Context, const ASSUME: Assume = { Assume::NOTHING }>
18 /// What transmutation safety conditions shall the compiler assume that *you* are checking?
19 #[unstable(feature = "transmutability", issue = "99571")]
20 #[cfg_attr(not(bootstrap), lang = "transmute_opts")]
21 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
23 /// When `true`, the compiler assumes that *you* are ensuring (either dynamically or statically) that
24 /// destination referents do not have stricter alignment requirements than source referents.
27 /// When `true`, the compiler assume that *you* are ensuring that lifetimes are not extended in a manner
28 /// that violates Rust's memory model.
31 /// When `true`, the compiler assumes that *you* have ensured that it is safe for you to violate the
32 /// type and field privacy of the destination type (and sometimes of the source type, too).
35 /// When `true`, the compiler assumes that *you* are ensuring that the source type is actually a valid
36 /// instance of the destination type.
41 /// Do not assume that *you* have ensured any safety properties are met.
42 #[unstable(feature = "transmutability", issue = "99571")]
43 pub const NOTHING: Self =
44 Self { alignment: false, lifetimes: false, safety: false, validity: false };
46 /// Assume only that alignment conditions are met.
47 #[unstable(feature = "transmutability", issue = "99571")]
48 pub const ALIGNMENT: Self = Self { alignment: true, ..Self::NOTHING };
50 /// Assume only that lifetime conditions are met.
51 #[unstable(feature = "transmutability", issue = "99571")]
52 pub const LIFETIMES: Self = Self { lifetimes: true, ..Self::NOTHING };
54 /// Assume only that safety conditions are met.
55 #[unstable(feature = "transmutability", issue = "99571")]
56 pub const SAFETY: Self = Self { safety: true, ..Self::NOTHING };
58 /// Assume only that dynamically-satisfiable validity conditions are met.
59 #[unstable(feature = "transmutability", issue = "99571")]
60 pub const VALIDITY: Self = Self { validity: true, ..Self::NOTHING };
62 /// Assume both `self` and `other_assumptions`.
63 #[unstable(feature = "transmutability", issue = "99571")]
64 pub const fn and(self, other_assumptions: Self) -> Self {
66 alignment: self.alignment || other_assumptions.alignment,
67 lifetimes: self.lifetimes || other_assumptions.lifetimes,
68 safety: self.safety || other_assumptions.safety,
69 validity: self.validity || other_assumptions.validity,
73 /// Assume `self`, excepting `other_assumptions`.
74 #[unstable(feature = "transmutability", issue = "99571")]
75 pub const fn but_not(self, other_assumptions: Self) -> Self {
77 alignment: self.alignment && !other_assumptions.alignment,
78 lifetimes: self.lifetimes && !other_assumptions.lifetimes,
79 safety: self.safety && !other_assumptions.safety,
80 validity: self.validity && !other_assumptions.validity,
85 // FIXME(jswrenn): This const op is not actually usable. Why?
86 // https://github.com/rust-lang/rust/pull/100726#issuecomment-1219928926
87 #[unstable(feature = "transmutability", issue = "99571")]
88 #[rustc_const_unstable(feature = "transmutability", issue = "99571")]
89 impl const core::ops::Add for Assume {
92 fn add(self, other_assumptions: Assume) -> Assume {
93 self.and(other_assumptions)
97 // FIXME(jswrenn): This const op is not actually usable. Why?
98 // https://github.com/rust-lang/rust/pull/100726#issuecomment-1219928926
99 #[unstable(feature = "transmutability", issue = "99571")]
100 #[rustc_const_unstable(feature = "transmutability", issue = "99571")]
101 impl const core::ops::Sub for Assume {
102 type Output = Assume;
104 fn sub(self, other_assumptions: Assume) -> Assume {
105 self.but_not(other_assumptions)