diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs index d3b8a60b797..e0aa25724c1 100644 --- a/src/libcore/mem.rs +++ b/src/libcore/mem.rs @@ -15,7 +15,12 @@ #![stable(feature = "rust1", since = "1.0.0")] +use clone; +use cmp; +use fmt; +use hash; use intrinsics; +use marker::{Copy, PhantomData, Sized}; use ptr; #[stable(feature = "rust1", since = "1.0.0")] @@ -647,3 +652,80 @@ pub fn drop(_x: T) { } pub unsafe fn transmute_copy(src: &T) -> U { ptr::read(src as *const T as *const U) } + +/// Opaque type representing the discriminant of an enum. +/// +/// See the `discriminant` function in this module for more information. +#[unstable(feature = "discriminant_value", reason = "recently added, follows RFC", issue = "24263")] +pub struct Discriminant(u64, PhantomData<*const T>); + +// N.B. These trait implementations cannot be derived because we don't want any bounds on T. + +#[unstable(feature = "discriminant_value", reason = "recently added, follows RFC", issue = "24263")] +impl Copy for Discriminant {} + +#[unstable(feature = "discriminant_value", reason = "recently added, follows RFC", issue = "24263")] +impl clone::Clone for Discriminant { + fn clone(&self) -> Self { + *self + } +} + +#[unstable(feature = "discriminant_value", reason = "recently added, follows RFC", issue = "24263")] +impl cmp::PartialEq for Discriminant { + fn eq(&self, rhs: &Self) -> bool { + self.0 == rhs.0 + } +} + +#[unstable(feature = "discriminant_value", reason = "recently added, follows RFC", issue = "24263")] +impl cmp::Eq for Discriminant {} + +#[unstable(feature = "discriminant_value", reason = "recently added, follows RFC", issue = "24263")] +impl hash::Hash for Discriminant { + fn hash(&self, state: &mut H) { + self.0.hash(state); + } +} + +#[unstable(feature = "discriminant_value", reason = "recently added, follows RFC", issue = "24263")] +impl fmt::Debug for Discriminant { + fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { + fmt.debug_tuple("Discriminant") + .field(&self.0) + .finish() + } +} + +/// Returns a value uniquely identifying the enum variant in `v`. +/// +/// If `T` is not an enum, calling this function will not result in undefined behavior, but the +/// return value is unspecified. +/// +/// # Stability +/// +/// The discriminant of an enum variant may change if the enum definition changes. A discriminant +/// of some variant will not change between compilations with the same compiler. +/// +/// # Examples +/// +/// This can be used to compare enums that carry data, while disregarding +/// the actual data: +/// +/// ``` +/// #![feature(discriminant_value)] +/// use std::mem; +/// +/// enum Foo { A(&'static str), B(i32), C(i32) } +/// +/// assert!(mem::discriminant(&Foo::A("bar")) == mem::discriminant(&Foo::A("baz"))); +/// assert!(mem::discriminant(&Foo::B(1)) == mem::discriminant(&Foo::B(2))); +/// assert!(mem::discriminant(&Foo::B(3)) != mem::discriminant(&Foo::C(3))); +/// ``` +#[unstable(feature = "discriminant_value", reason = "recently added, follows RFC", issue = "24263")] +pub fn discriminant(v: &T) -> Discriminant { + unsafe { + Discriminant(intrinsics::discriminant_value(v), PhantomData) + } +} + diff --git a/src/test/run-pass/discriminant_value-wrapper.rs b/src/test/run-pass/discriminant_value-wrapper.rs new file mode 100644 index 00000000000..2dbda0be18d --- /dev/null +++ b/src/test/run-pass/discriminant_value-wrapper.rs @@ -0,0 +1,28 @@ +// Copyright 2016 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +#![feature(discriminant_value)] + +use std::mem; + +enum ADT { + First(u32, u32), + Second(u64) +} + +pub fn main() { + assert!(mem::discriminant(&ADT::First(0,0)) == mem::discriminant(&ADT::First(1,1))); + assert!(mem::discriminant(&ADT::Second(5)) == mem::discriminant(&ADT::Second(6))); + assert!(mem::discriminant(&ADT::First(2,2)) != mem::discriminant(&ADT::Second(2))); + + let _ = mem::discriminant(&10); + let _ = mem::discriminant(&"test"); +} +