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comment `instantiate_poly_trait_ref` and its binder behavior

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nikomatsakis authored and alexreg committed May 31, 2019
1 parent f6ee542 commit 83078f0b37fd944f09bcfce4f8d476814b936aae
Showing with 19 additions and 0 deletions.
  1. +19 −0 src/librustc_typeck/astconv.rs
@@ -792,6 +792,25 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
(poly_trait_ref, potential_assoc_types)
}

/// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
/// a full trait reference. The resulting trait reference is returned. This may also generate
/// auxiliary bounds, which are added to `bounds`.
///
/// Example:
///
/// ```
/// poly_trait_ref = Iterator<Item = u32>
/// self_ty = Foo
/// ```
///
/// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
///
/// **A note on binders:** against our usual convention, there is an implied bounder around
/// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
/// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
/// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
/// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
/// however.
pub fn instantiate_poly_trait_ref(&self,
poly_trait_ref: &hir::PolyTraitRef,
self_ty: Ty<'tcx>,

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