[][src]Struct rustc::ty::subst::SubstFolder

struct SubstFolder<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
    tcx: TyCtxt<'a, 'gcx, 'tcx>,
    substs: &'a [Kind<'tcx>],
    span: Option<Span>,
    root_ty: Option<Ty<'tcx>>,
    ty_stack_depth: usize,
    region_binders_passed: u32,
}
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Fields

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🔬 This is a nightly-only experimental API. (rustc_private)

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🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

🔬 This is a nightly-only experimental API. (rustc_private)

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Methods

impl<'a, 'gcx, 'tcx> SubstFolder<'a, 'gcx, 'tcx>
[src]

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🔬 This is a nightly-only experimental API. (rustc_private)

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It is sometimes necessary to adjust the debruijn indices during substitution. This occurs when we are substituting a type with escaping regions into a context where we have passed through region binders. That's quite a mouthful. Let's see an example:

type Func<A> = fn(A);
type MetaFunc = for<'a> fn(Func<&'a int>)

The type MetaFunc, when fully expanded, will be

for<'a> fn(fn(&'a int))
        ^~ ^~ ^~~
        |  |  |
        |  |  DebruijnIndex of 2
        Binders

Here the 'a lifetime is bound in the outer function, but appears as an argument of the inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip over the inner binder (remember that we count Debruijn indices from 1). However, in the definition of MetaFunc, the binder is not visible, so the type &'a int will have a debruijn index of 1. It's only during the substitution that we can see we must increase the depth by 1 to account for the binder that we passed through.

As a second example, consider this twist:

type FuncTuple<A> = (A,fn(A));
type MetaFuncTuple = for<'a> fn(FuncTuple<&'a int>)

Here the final type will be:

for<'a> fn((&'a int, fn(&'a int)))
            ^~~         ^~~
            |           |
     DebruijnIndex of 1 |
                 DebruijnIndex of 2

As indicated in the diagram, here the same type &'a int is substituted once, but in the first case we do not increase the Debruijn index and in the second case we do. The reason is that only in the second case have we passed through a fn binder.

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Trait Implementations

impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for SubstFolder<'a, 'gcx, 'tcx>
[src]

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🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

🔬 This is a nightly-only experimental API. (rustc_private)

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Auto Trait Implementations

impl<'a, 'gcx, 'tcx> !Send for SubstFolder<'a, 'gcx, 'tcx>

impl<'a, 'gcx, 'tcx> !Sync for SubstFolder<'a, 'gcx, 'tcx>

Blanket Implementations

impl<T> MaybeResult for T
[src]

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🔬 This is a nightly-only experimental API. (rustc_private)

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impl<'a, T> Captures for T where
    T: ?Sized
[src]

impl<T> From for T
[src]

Performs the conversion.

impl<T, U> Into for T where
    U: From<T>, 
[src]

Performs the conversion.

impl<T, U> TryFrom for T where
    T: From<U>, 
[src]

🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from)

Performs the conversion.

impl<T> Borrow for T where
    T: ?Sized
[src]

Important traits for &'a mut R

Immutably borrows from an owned value. Read more

impl<T, U> TryInto for T where
    U: TryFrom<T>, 
[src]

🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from)

Performs the conversion.

impl<T> BorrowMut for T where
    T: ?Sized
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Important traits for &'a mut R

Mutably borrows from an owned value. Read more

impl<T> Any for T where
    T: 'static + ?Sized
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this method will likely be replaced by an associated static

Gets the TypeId of self. Read more

impl<E> SpecializationError for E
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Create an error for a missing method specialization. Defaults to panicking with type, trait & method names. S is the encoder/decoder state type, T is the type being encoded/decoded, and the arguments are the names of the trait and method that should've been overridden. Read more

impl<T> Erased for T
[src]

impl<T> Send for T where
    T: ?Sized
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impl<T> Sync for T where
    T: ?Sized
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impl<T> Erased for T