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@ -64,13 +64,13 @@ For instance `Vec` is a type constructor that takes a `T` and returns a
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`Vec<T>`. `&` and `&mut` are type constructors that take two inputs: a
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lifetime, and a type to point to.
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A type constructor's *variance* is how the subtyping of its inputs affects the
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A type constructor F's *variance* is how the subtyping of its inputs affects the
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subtyping of its outputs. There are three kinds of variance in Rust:
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* F is *covariant* over `T` if `T` being a subtype of `U` implies
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`F<T>` is a subtype of `F<U>` (subtyping "passes through")
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* F is *contravariant* over `T` if `T` being a subtype of `U` implies
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`F<U>` is a subtype of `F<U>` (subtyping is "inverted")
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`F<U>` is a subtype of `F<T>` (subtyping is "inverted")
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* F is *invariant* over `T` otherwise (no subtyping relation can be derived)
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It should be noted that covariance is *far* more common and important than
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