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Allow marker types to have unsized parameters #20014

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Merged
merged 1 commit into from
Dec 22, 2014
Merged

Allow marker types to have unsized parameters #20014

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30 changes: 20 additions & 10 deletions src/libcore/kinds.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -91,7 +91,8 @@ pub trait Sync for Sized? {
/// implemented using unsafe code. In that case, you may want to embed
/// some of the marker types below into your type.
pub mod marker {
use super::Copy;
use super::{Copy,Sized};
use clone::Clone;

/// A marker type whose type parameter `T` is considered to be
/// covariant with respect to the type itself. This is (typically)
Expand Down Expand Up @@ -131,10 +132,13 @@ pub mod marker {
/// (for example, `S<&'static int>` is a subtype of `S<&'a int>`
/// for some lifetime `'a`, but not the other way around).
#[lang="covariant_type"]
#[deriving(Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct CovariantType<T>;
#[deriving(PartialEq, Eq, PartialOrd, Ord)]
pub struct CovariantType<Sized? T>;

impl<T> Copy for CovariantType<T> {}
impl<Sized? T> Copy for CovariantType<T> {}
impl<Sized? T> Clone for CovariantType<T> {
fn clone(&self) -> CovariantType<T> { *self }
}

/// A marker type whose type parameter `T` is considered to be
/// contravariant with respect to the type itself. This is (typically)
Expand Down Expand Up @@ -176,10 +180,13 @@ pub mod marker {
/// function requires arguments of type `T`, it must also accept
/// arguments of type `U`, hence such a conversion is safe.
#[lang="contravariant_type"]
#[deriving(Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct ContravariantType<T>;
#[deriving(PartialEq, Eq, PartialOrd, Ord)]
pub struct ContravariantType<Sized? T>;

impl<T> Copy for ContravariantType<T> {}
impl<Sized? T> Copy for ContravariantType<T> {}
impl<Sized? T> Clone for ContravariantType<T> {
fn clone(&self) -> ContravariantType<T> { *self }
}

/// A marker type whose type parameter `T` is considered to be
/// invariant with respect to the type itself. This is (typically)
Expand All @@ -203,10 +210,13 @@ pub mod marker {
/// never written, but in fact `Cell` uses unsafe code to achieve
/// interior mutability.
#[lang="invariant_type"]
#[deriving(Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct InvariantType<T>;
#[deriving(PartialEq, Eq, PartialOrd, Ord)]
pub struct InvariantType<Sized? T>;

impl<T> Copy for InvariantType<T> {}
impl<Sized? T> Copy for InvariantType<T> {}
impl<Sized? T> Clone for InvariantType<T> {
fn clone(&self) -> InvariantType<T> { *self }
}

/// As `CovariantType`, but for lifetime parameters. Using
/// `CovariantLifetime<'a>` indicates that it is ok to substitute
Expand Down