Key in rustc_middle::query - Rust (original) (raw)

pub trait Key: Sized {
    type Cache<V>;

    // Required method
    fn default_span(&self, tcx: TyCtxt<'_>) -> Span;

    // Provided methods
    fn key_as_def_id(&self) -> Option<DefId> { ... }
    fn def_id_for_ty_in_cycle(&self) -> Option<DefId> { ... }
}

Expand description

The Key trait controls what types can legally be used as the key for a query.

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The type of in-memory cache to use for queries with this key type.

In practice the cache type must implement QueryCache, though that constraint is not enforced here.

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In the event that a cycle occurs, if no explicit span has been given for a query with key self, what span should we use?

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If the key is a DefId or DefId–equivalent, return that DefId. Otherwise, return None.

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Used to detect when ADT def ids are used as keys in a cycle for better error reporting.

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

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