// Copyright 2012 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 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. use super::combine::*; use super::lattice::*; use super::higher_ranked::HigherRankedRelations; use super::{cres}; use super::Subtype; use middle::ty::{BuiltinBounds}; use middle::ty::{self, Ty}; use syntax::ast::{MutImmutable, MutMutable, Unsafety}; use util::ppaux::mt_to_string; use util::ppaux::Repr; /// "Greatest lower bound" (common subtype) pub struct Glb<'f, 'tcx: 'f> { fields: CombineFields<'f, 'tcx> } #[allow(non_snake_case)] pub fn Glb<'f, 'tcx>(cf: CombineFields<'f, 'tcx>) -> Glb<'f, 'tcx> { Glb { fields: cf } } impl<'f, 'tcx> Combine<'tcx> for Glb<'f, 'tcx> { fn tag(&self) -> String { "Glb".to_string() } fn fields<'a>(&'a self) -> &'a CombineFields<'a, 'tcx> { &self.fields } fn tys_with_variance(&self, v: ty::Variance, a: Ty<'tcx>, b: Ty<'tcx>) -> cres<'tcx, Ty<'tcx>> { match v { ty::Invariant => self.equate().tys(a, b), ty::Covariant => self.tys(a, b), ty::Bivariant => self.bivariate().tys(a, b), ty::Contravariant => self.lub().tys(a, b), } } fn regions_with_variance(&self, v: ty::Variance, a: ty::Region, b: ty::Region) -> cres<'tcx, ty::Region> { match v { ty::Invariant => self.equate().regions(a, b), ty::Covariant => self.regions(a, b), ty::Bivariant => self.bivariate().regions(a, b), ty::Contravariant => self.lub().regions(a, b), } } fn mts(&self, a: &ty::mt<'tcx>, b: &ty::mt<'tcx>) -> cres<'tcx, ty::mt<'tcx>> { let tcx = self.fields.infcx.tcx; debug!("{}.mts({}, {})", self.tag(), mt_to_string(tcx, a), mt_to_string(tcx, b)); match (a.mutbl, b.mutbl) { // If one side or both is mut, then the GLB must use // the precise type from the mut side. (MutMutable, MutMutable) => { let t = try!(self.equate().tys(a.ty, b.ty)); Ok(ty::mt {ty: t, mutbl: MutMutable}) } // If one side or both is immutable, we can use the GLB of // both sides but mutbl must be `MutImmutable`. (MutImmutable, MutImmutable) => { let t = try!(self.tys(a.ty, b.ty)); Ok(ty::mt {ty: t, mutbl: MutImmutable}) } // There is no mutual subtype of these combinations. (MutMutable, MutImmutable) | (MutImmutable, MutMutable) => { Err(ty::terr_mutability) } } } fn unsafeties(&self, a: Unsafety, b: Unsafety) -> cres<'tcx, Unsafety> { match (a, b) { (Unsafety::Normal, _) | (_, Unsafety::Normal) => Ok(Unsafety::Normal), (Unsafety::Unsafe, Unsafety::Unsafe) => Ok(Unsafety::Unsafe) } } fn builtin_bounds(&self, a: ty::BuiltinBounds, b: ty::BuiltinBounds) -> cres<'tcx, ty::BuiltinBounds> { // More bounds is a subtype of fewer bounds, so // the GLB (mutual subtype) is the union. Ok(a.union(b)) } fn regions(&self, a: ty::Region, b: ty::Region) -> cres<'tcx, ty::Region> { debug!("{}.regions({}, {})", self.tag(), a.repr(self.fields.infcx.tcx), b.repr(self.fields.infcx.tcx)); Ok(self.fields.infcx.region_vars.glb_regions(Subtype(self.trace()), a, b)) } fn tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> cres<'tcx, Ty<'tcx>> { super_lattice_tys(self, a, b) } fn binders(&self, a: &ty::Binder, b: &ty::Binder) -> cres<'tcx, ty::Binder> where T : Combineable<'tcx> { self.higher_ranked_glb(a, b) } }