| // 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 <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. |
| |
| //! # Lattice Variables |
| //! |
| //! This file contains generic code for operating on inference variables |
| //! that are characterized by an upper- and lower-bound. The logic and |
| //! reasoning is explained in detail in the large comment in `infer.rs`. |
| //! |
| //! The code in here is defined quite generically so that it can be |
| //! applied both to type variables, which represent types being inferred, |
| //! and fn variables, which represent function types being inferred. |
| //! It may eventually be applied to their types as well, who knows. |
| //! In some cases, the functions are also generic with respect to the |
| //! operation on the lattice (GLB vs LUB). |
| //! |
| //! Although all the functions are generic, we generally write the |
| //! comments in a way that is specific to type variables and the LUB |
| //! operation. It's just easier that way. |
| //! |
| //! In general all of the functions are defined parametrically |
| //! over a `LatticeValue`, which is a value defined with respect to |
| //! a lattice. |
| |
| use super::InferCtxt; |
| |
| use ty::TyVar; |
| use ty::{self, Ty}; |
| use ty::relate::{RelateResult, TypeRelation}; |
| |
| pub trait LatticeDir<'f, 'gcx: 'f+'tcx, 'tcx: 'f> : TypeRelation<'f, 'gcx, 'tcx> { |
| fn infcx(&self) -> &'f InferCtxt<'f, 'gcx, 'tcx>; |
| |
| // Relates the type `v` to `a` and `b` such that `v` represents |
| // the LUB/GLB of `a` and `b` as appropriate. |
| fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()>; |
| } |
| |
| pub fn super_lattice_tys<'a, 'gcx, 'tcx, L>(this: &mut L, |
| a: Ty<'tcx>, |
| b: Ty<'tcx>) |
| -> RelateResult<'tcx, Ty<'tcx>> |
| where L: LatticeDir<'a, 'gcx, 'tcx>, 'gcx: 'a+'tcx, 'tcx: 'a |
| { |
| debug!("{}.lattice_tys({:?}, {:?})", |
| this.tag(), |
| a, |
| b); |
| |
| if a == b { |
| return Ok(a); |
| } |
| |
| let infcx = this.infcx(); |
| let a = infcx.type_variables.borrow_mut().replace_if_possible(a); |
| let b = infcx.type_variables.borrow_mut().replace_if_possible(b); |
| match (&a.sty, &b.sty) { |
| (&ty::TyInfer(TyVar(..)), &ty::TyInfer(TyVar(..))) |
| if infcx.type_var_diverges(a) && infcx.type_var_diverges(b) => { |
| let v = infcx.next_diverging_ty_var(); |
| this.relate_bound(v, a, b)?; |
| Ok(v) |
| } |
| |
| (&ty::TyInfer(TyVar(..)), _) | |
| (_, &ty::TyInfer(TyVar(..))) => { |
| let v = infcx.next_ty_var(); |
| this.relate_bound(v, a, b)?; |
| Ok(v) |
| } |
| |
| _ => { |
| infcx.super_combine_tys(this, a, b) |
| } |
| } |
| } |