src/librustc_mir/build/expr/as_constant.rs

   1 // Copyright 2015 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.
   4 //
   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.
  10
  11 //! See docs in build/expr/mod.rs
  12
  13 use build::Builder;
  14 use hair::*;
  15 use rustc::mir::*;
  16
  17 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  18     /// Compile `expr`, yielding a compile-time constant. Assumes that
  19     /// `expr` is a valid compile-time constant!
  20     pub fn as_constant<M>(&mut self, expr: M) -> Constant<'tcx>
  21         where M: Mirror<'tcx, Output=Expr<'tcx>>
  22     {
  23         let expr = self.hir.mirror(expr);
  24         self.expr_as_constant(expr)
  25     }
  26
  27     fn expr_as_constant(&mut self, expr: Expr<'tcx>) -> Constant<'tcx> {
  28         let this = self;
  29         let Expr { ty, temp_lifetime: _, span, kind } = expr;
  30         match kind {
  31             ExprKind::Scope { extent: _, value } =>
  32                 this.as_constant(value),
  33             ExprKind::Literal { literal } =>
  34                 Constant { span: span, ty: ty, literal: literal },
  35             _ =>
  36                 span_bug!(
  37                     span,
  38                     "expression is not a valid constant {:?}",
  39                     kind),
  40         }
  41     }
  42 }