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// Copyright 2013 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. 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, } }