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https://github.com/rust-lang/rust
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Deprecate MarkerTrait and PhantomFn.
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@ -192,13 +192,16 @@ struct TyDesc {
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align: usize
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}
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trait AllTypes { fn dummy(&self) { } }
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impl<T:?Sized> AllTypes for T { }
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unsafe fn get_tydesc<T>() -> *const TyDesc {
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use std::raw::TraitObject;
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let ptr = &*(1 as *const T);
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// Can use any trait that is implemented for all types.
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let obj = mem::transmute::<&marker::MarkerTrait, TraitObject>(ptr);
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let obj = mem::transmute::<&AllTypes, TraitObject>(ptr);
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obj.vtable as *const TyDesc
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}
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@ -35,6 +35,7 @@
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#[stable(feature = "rust1", since = "1.0.0")]
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#[lang="send"]
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#[rustc_on_unimplemented = "`{Self}` cannot be sent between threads safely"]
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#[allow(deprecated)]
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pub unsafe trait Send : MarkerTrait {
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// empty.
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}
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@ -50,6 +51,7 @@ impl !Send for Managed { }
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#[lang="sized"]
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#[rustc_on_unimplemented = "`{Self}` does not have a constant size known at compile-time"]
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#[fundamental] // for Default, for example, which requires that `[T]: !Default` be evaluatable
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#[allow(deprecated)]
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pub trait Sized : MarkerTrait {
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// Empty.
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}
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@ -203,6 +205,7 @@ pub trait Copy : Clone {
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#[stable(feature = "rust1", since = "1.0.0")]
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#[lang="sync"]
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#[rustc_on_unimplemented = "`{Self}` cannot be shared between threads safely"]
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#[allow(deprecated)]
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pub unsafe trait Sync : MarkerTrait {
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// Empty
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}
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@ -269,14 +272,10 @@ fn clone(&self) -> $t<T> {
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)
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}
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/// `MarkerTrait` is intended to be used as the supertrait for traits
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/// that don't have any methods but instead serve just to designate
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/// categories of types. An example would be the `Send` trait, which
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/// indicates types that are sendable: `Send` does not itself offer
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/// any methods, but instead is used to gate access to data.
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///
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/// FIXME. Better documentation needed here!
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#[stable(feature = "rust1", since = "1.0.0")]
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/// `MarkerTrait` is deprecated and no longer needed.
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#[unstable(feature = "core", reason = "deprecated")]
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#[deprecated(since = "1.0.0", reason = "No longer needed")]
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#[allow(deprecated)]
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pub trait MarkerTrait : PhantomFn<Self,Self> { }
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// ~~~~~ <-- FIXME(#22806)?
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//
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@ -284,68 +283,13 @@ pub trait MarkerTrait : PhantomFn<Self,Self> { }
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// but we should ideally solve the underlying problem. That's a bit
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// complicated.
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#[allow(deprecated)]
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impl<T:?Sized> MarkerTrait for T { }
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/// `PhantomFn` is a marker trait for use with traits that contain
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/// type or lifetime parameters that do not appear in any of their
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/// methods. In that case, you can either remove those parameters, or
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/// add a `PhantomFn` supertrait that reflects the signature of
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/// methods that compiler should "pretend" exists. This most commonly
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/// occurs for traits with no methods: in that particular case, you
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/// can extend `MarkerTrait`, which is equivalent to
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/// `PhantomFn<Self>`.
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///
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/// # Examples
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///
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/// As an example, consider a trait with no methods like `Even`, meant
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/// to represent types that are "even":
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///
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/// ```rust,ignore
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/// trait Even { }
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/// ```
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///
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/// In this case, because the implicit parameter `Self` is unused, the
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/// compiler will issue an error. The only purpose of this trait is to
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/// categorize types (and hence instances of those types) as "even" or
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/// not, so if we *were* going to have a method, it might look like:
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///
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/// ```rust,ignore
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/// trait Even {
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/// fn is_even(self) -> bool { true }
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/// }
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/// ```
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///
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/// Therefore, we can model a method like this as follows:
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///
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/// ```
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/// use std::marker::PhantomFn;
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/// trait Even : PhantomFn<Self> { }
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/// ```
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///
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/// Another equivalent, but clearer, option would be to use
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/// `MarkerTrait`:
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///
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/// ```
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/// # #![feature(core)]
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/// use std::marker::MarkerTrait;
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/// trait Even : MarkerTrait { }
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/// ```
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///
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/// # Parameters
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///
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/// - `A` represents the type of the method's argument. You can use a
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/// tuple to represent "multiple" arguments. Any types appearing here
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/// will be considered "contravariant".
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/// - `R`, if supplied, represents the method's return type. This defaults
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/// to `()` as it is rarely needed.
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///
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/// # Additional reading
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///
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/// More details and background can be found in [RFC 738][738].
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///
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/// [738]: https://github.com/rust-lang/rfcs/blob/master/text/0738-variance.md
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/// `PhantomFn` is a deprecated marker trait that is no longer needed.
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#[lang="phantom_fn"]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[unstable(feature = "core", reason = "deprecated")]
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#[deprecated(since = "1.0.0", reason = "No longer needed")]
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pub trait PhantomFn<A:?Sized,R:?Sized=()> { }
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/// `PhantomData<T>` allows you to describe that a type acts as if it stores a value of type `T`,
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@ -444,6 +388,7 @@ unsafe impl<'a, T: Send + ?Sized> Send for &'a mut T {}
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/// [1]: http://en.wikipedia.org/wiki/Parametricity
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#[rustc_reflect_like]
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#[unstable(feature = "core", reason = "requires RFC and more experience")]
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#[allow(deprecated)]
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pub trait Reflect : MarkerTrait {
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}
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@ -14,6 +14,7 @@
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use ops::Deref;
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/// Unsafe trait to indicate what types are usable with the NonZero struct
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#[allow(deprecated)]
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pub unsafe trait Zeroable : MarkerTrait {}
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unsafe impl<T:?Sized> Zeroable for *const T {}
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