| use rustc::ty; |
| |
| pub fn glb(v1: ty::Variance, v2: ty::Variance) -> ty::Variance { |
| // Greatest lower bound of the variance lattice as |
| // defined in The Paper: |
| // |
| // * |
| // - + |
| // o |
| match (v1, v2) { |
| (ty::Invariant, _) | |
| (_, ty::Invariant) => ty::Invariant, |
| |
| (ty::Covariant, ty::Contravariant) => ty::Invariant, |
| (ty::Contravariant, ty::Covariant) => ty::Invariant, |
| |
| (ty::Covariant, ty::Covariant) => ty::Covariant, |
| |
| (ty::Contravariant, ty::Contravariant) => ty::Contravariant, |
| |
| (x, ty::Bivariant) | |
| (ty::Bivariant, x) => x, |
| } |
| } |