[][src]Struct rustc::traits::ProjectionCache

pub struct ProjectionCache<'tcx> {
    map: SnapshotMap<ProjectionCacheKey<'tcx>, ProjectionCacheEntry<'tcx>>,
}
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The projection cache. Unlike the standard caches, this can include infcx-dependent type variables - therefore, we have to roll the cache back each time we roll a snapshot back, to avoid assumptions on yet-unresolved inference variables. Types with skolemized regions also have to be removed when the respective snapshot ends.

Because of that, projection cache entries can be "stranded" and left inaccessible when type variables inside the key are resolved. We make no attempt to recover or remove "stranded" entries, but rather let them be (for the lifetime of the infcx).

Entries in the projection cache might contain inference variables that will be resolved by obligations on the projection cache entry - e.g. when a type parameter in the associated type is constrained through an "RFC 447" projection on the impl.

When working with a fulfillment context, the derived obligations of each projection cache entry will be registered on the fulfillcx, so any users that can wait for a fulfillcx fixed point need not care about this. However, users that don't wait for a fixed point (e.g. trait evaluation) have to resolve the obligations themselves to make sure the projected result is ok and avoid issues like #43132.

If that is done, after evaluation the obligations, it is a good idea to call ProjectionCache::complete to make sure the obligations won't be re-evaluated and avoid an exponential worst-case.

FIXME: we probably also want some sort of cross-infcx cache here to reduce the amount of duplication. Let's see what we get with the Chalk reforms.

Fields

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Methods

impl<'tcx> ProjectionCache<'tcx>
[src]

🔬 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)

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?

Try to start normalize key; returns an error if normalization already occurred (this error corresponds to a cache hit, so it's actually a good thing).

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Indicates that key was normalized to value.

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Mark the relevant projection cache key as having its derived obligations complete, so they won't have to be re-computed (this is OK to do in a snapshot - if the snapshot is rolled back, the obligations will be marked as incomplete again).

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A specialized version of complete for when the key's value is known to be a NormalizedTy.

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Indicates that trying to normalize key resulted in ambiguity. No point in trying it again then until we gain more type information (in which case, the "fully resolved" key will be different).

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Indicates that trying to normalize key resulted in error.

Auto Trait Implementations

impl<'tcx> !Send for ProjectionCache<'tcx>

impl<'tcx> !Sync for ProjectionCache<'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
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impl<T> From for T
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Performs the conversion.

impl<T, U> Into for T where
    U: From<T>, 
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Performs the conversion.

impl<T, U> TryFrom for T where
    T: From<U>, 
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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
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Important traits for &'a mut R

Immutably borrows from an owned value. Read more

impl<T, U> TryInto for T where
    U: TryFrom<T>, 
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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
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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