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use rustc::ty;
pub trait Xform {
fn xform(self, v: Self) -> Self;
}
impl Xform for ty::Variance {
fn xform(self, v: ty::Variance) -> ty::Variance {
match (self, v) {
(ty::Covariant, ty::Covariant) => ty::Covariant,
(ty::Covariant, ty::Contravariant) => ty::Contravariant,
(ty::Covariant, ty::Invariant) => ty::Invariant,
(ty::Covariant, ty::Bivariant) => ty::Bivariant,
(ty::Contravariant, ty::Covariant) => ty::Contravariant,
(ty::Contravariant, ty::Contravariant) => ty::Covariant,
(ty::Contravariant, ty::Invariant) => ty::Invariant,
(ty::Contravariant, ty::Bivariant) => ty::Bivariant,
(ty::Invariant, _) => ty::Invariant,
(ty::Bivariant, _) => ty::Bivariant,
}
}
}
pub fn glb(v1: ty::Variance, v2: ty::Variance) -> ty::Variance {
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,
}
}