Struct rustc_trait_selection::infer::nll_relate::TypeRelating

pub struct TypeRelating<'me, 'tcx, D> where
    D: TypeRelatingDelegate<'tcx>,  {
    infcx: &'me InferCtxt<'me, 'tcx>,
    delegate: D,
    ambient_variance: Variance,
    a_scopes: Vec<BoundRegionScope<'tcx>, Global>,
    b_scopes: Vec<BoundRegionScope<'tcx>, Global>,
}

Fields

infcx: &'me InferCtxt<'me, 'tcx>

delegate: D

Callback to use when we deduce an outlives relationship.

ambient_variance: Variance

How are we relating a and b?

• Covariant means a <: b.
• Contravariant means b <: a.
• Invariant means `a == b.
• Bivariant means that it doesn’t matter.

a_scopes: Vec<BoundRegionScope<'tcx>, Global>

When we pass through a set of binders (e.g., when looking into a fn type), we push a new bound region scope onto here. This will contain the instantiated region for each region in those binders. When we then encounter a ReLateBound(d, br), we can use the De Bruijn index d to find the right scope, and then bound region name br to find the specific instantiation from within that scope. See replace_bound_region.

This field stores the instantiations for late-bound regions in the a type.

b_scopes: Vec<BoundRegionScope<'tcx>, Global>

Same as a_scopes, but for the b type.