src/test/run-pass-fulldeps/dropck_tarena_sound_drop.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 // Check that an arena (TypedArena) can carry elements whose drop
  12 // methods might access borrowed data, as long as the borrowed data
  13 // has lifetime that strictly outlives the arena itself.
  14 //
  15 // Compare against compile-fail/dropck_tarena_unsound_drop.rs, which
  16 // shows a similar setup, but restricts `f` so that the struct `C<'a>`
  17 // is force-fed a lifetime equal to that of the borrowed arena.
  18
  19 #![allow(unstable)]
  20 #![feature(rustc_private)]
  21
  22 extern crate arena;
  23
  24 use arena::TypedArena;
  25
  26 trait HasId { fn count(&self) -> usize; }
  27
  28 struct CheckId<T:HasId> { v: T }
  29
  30 // In the code below, the impl of HasId for `&'a usize` does not
  31 // actually access the borrowed data, but the point is that the
  32 // interface to CheckId does not (and cannot) know that, and therefore
  33 // when encountering the a value V of type CheckId<S>, we must
  34 // conservatively force the type S to strictly outlive V.
  35 impl<T:HasId> Drop for CheckId<T> {
  36     fn drop(&mut self) {
  37         assert!(self.v.count() > 0);
  38     }
  39 }
  40
  41 struct C<'a> { _v: CheckId<&'a usize>, }
  42
  43 impl<'a> HasId for &'a usize { fn count(&self) -> usize { 1 } }
  44
  45 fn f<'a, 'b>(_arena: &'a TypedArena<C<'b>>) {}
  46
  47 fn main() {
  48     let arena: TypedArena<C> = TypedArena::new();
  49     f(&arena);
  50 }