1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! # Lattice Variables
13 //! This file contains generic code for operating on inference variables
14 //! that are characterized by an upper- and lower-bound. The logic and
15 //! reasoning is explained in detail in the large comment in `infer.rs`.
17 //! The code in here is defined quite generically so that it can be
18 //! applied both to type variables, which represent types being inferred,
19 //! and fn variables, which represent function types being inferred.
20 //! It may eventually be applied to their types as well, who knows.
21 //! In some cases, the functions are also generic with respect to the
22 //! operation on the lattice (GLB vs LUB).
24 //! Although all the functions are generic, we generally write the
25 //! comments in a way that is specific to type variables and the LUB
26 //! operation. It's just easier that way.
28 //! In general all of the functions are defined parametrically
29 //! over a `LatticeValue`, which is a value defined with respect to
33 use super::type_variable::TypeVariableOrigin;
35 use traits::ObligationCause;
38 use ty::relate::{RelateResult, TypeRelation};
40 pub trait LatticeDir<'f, 'gcx: 'f+'tcx, 'tcx: 'f> : TypeRelation<'f, 'gcx, 'tcx> {
41 fn infcx(&self) -> &'f InferCtxt<'f, 'gcx, 'tcx>;
43 fn cause(&self) -> &ObligationCause<'tcx>;
45 // Relates the type `v` to `a` and `b` such that `v` represents
46 // the LUB/GLB of `a` and `b` as appropriate.
47 fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()>;
50 pub fn super_lattice_tys<'a, 'gcx, 'tcx, L>(this: &mut L,
53 -> RelateResult<'tcx, Ty<'tcx>>
54 where L: LatticeDir<'a, 'gcx, 'tcx>, 'gcx: 'a+'tcx, 'tcx: 'a
56 debug!("{}.lattice_tys({:?}, {:?})",
65 let infcx = this.infcx();
66 let a = infcx.type_variables.borrow_mut().replace_if_possible(a);
67 let b = infcx.type_variables.borrow_mut().replace_if_possible(b);
68 match (&a.sty, &b.sty) {
69 (&ty::TyInfer(TyVar(..)), &ty::TyInfer(TyVar(..)))
70 if infcx.type_var_diverges(a) && infcx.type_var_diverges(b) => {
71 let v = infcx.next_diverging_ty_var(
72 TypeVariableOrigin::LatticeVariable(this.cause().span));
73 this.relate_bound(v, a, b)?;
77 (&ty::TyInfer(TyVar(..)), _) |
78 (_, &ty::TyInfer(TyVar(..))) => {
79 let v = infcx.next_ty_var(TypeVariableOrigin::LatticeVariable(this.cause().span));
80 this.relate_bound(v, a, b)?;
85 infcx.super_combine_tys(this, a, b)