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@ -346,17 +346,16 @@ impl<T:?Sized> MarkerTrait for T { }
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#[stable(feature = "rust1", since = "1.0.0")]
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pub trait PhantomFn<A:?Sized,R:?Sized=()> { }
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/// `PhantomData` is a way to tell the compiler about fake fields.
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/// Phantom data is required whenever type parameters are not used.
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/// The idea is that if the compiler encounters a `PhantomData<T>`
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/// instance, it will behave *as if* an instance of the type `T` were
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/// present for the purpose of various automatic analyses.
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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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/// even though it does not. This allows you to inform the compiler about certain safety properties
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/// of your code.
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///
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/// Though they both have scary names, `PhantomData<T>` and "phantom types" are unrelated. 👻👻👻
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///
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/// # Examples
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///
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/// When handling external resources over a foreign function interface, `PhantomData<T>` can
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/// prevent mismatches by enforcing types in the method implementations, although the struct
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/// doesn't actually contain values of the resource type.
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/// prevent mismatches by enforcing types in the method implementations:
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///
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/// ```
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/// # trait ResType { fn foo(&self); };
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@ -397,11 +396,6 @@ pub trait PhantomFn<A:?Sized,R:?Sized=()> { }
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/// commonly necessary if the structure is using an unsafe pointer
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/// like `*mut T` whose referent may be dropped when the type is
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/// dropped, as a `*mut T` is otherwise not treated as owned.
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///
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/// FIXME. Better documentation and examples of common patterns needed
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/// here! For now, please see [RFC 738][738] for more information.
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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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#[lang="phantom_data"]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct PhantomData<T:?Sized>;
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