src/test/run-pass/intrinsics/intrinsic-move-val.rs

   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.
   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 // run-pass
  12
  13 #![feature(box_syntax)]
  14 #![feature(intrinsics)]
  15
  16 mod rusti {
  17     extern "rust-intrinsic" {
  18         pub fn init<T>() -> T;
  19         pub fn move_val_init<T>(dst: *mut T, src: T);
  20     }
  21 }
  22
  23 pub fn main() {
  24     unsafe {
  25         // sanity check
  26         check_drops_state(0, None);
  27
  28         let mut x: Box<D> = box D(1);
  29         assert_eq!(x.0, 1);
  30
  31         // A normal overwrite, to demonstrate `check_drops_state`.
  32         x = box D(2);
  33
  34         // At this point, one destructor has run, because the
  35         // overwrite of `x` drops its initial value.
  36         check_drops_state(1, Some(1));
  37
  38         let mut y: Box<D> = rusti::init();
  39
  40         // An initial binding does not overwrite anything.
  41         check_drops_state(1, Some(1));
  42
  43         // Since `y` has been initialized via the `init` intrinsic, it
  44         // would be unsound to directly overwrite its value via normal
  45         // assignment.
  46         //
  47         // The code currently generated by the compiler is overly
  48         // accepting, however, in that it will check if `y` is itself
  49         // null and thus avoid the unsound action of attempting to
  50         // free null. In other words, if we were to do a normal
  51         // assignment like `y = box D(4);` here, it probably would not
  52         // crash today. But the plan is that it may well crash in the
  53         // future, (I believe).
  54
  55         // `x` is moved here; the manner in which this is tracked by the
  56         // compiler is hidden.
  57         rusti::move_val_init(&mut y, x);
  58
  59         // But what we *can* observe is how many times the destructor
  60         // for `D` is invoked, and what the last value we saw was
  61         // during such a destructor call. We do so after the end of
  62         // this scope.
  63
  64         assert_eq!(y.0, 2);
  65         y.0 = 3;
  66         assert_eq!(y.0, 3);
  67
  68         check_drops_state(1, Some(1));
  69     }
  70
  71     check_drops_state(2, Some(3));
  72 }
  73
  74 static mut NUM_DROPS: i32 = 0;
  75 static mut LAST_DROPPED: Option<i32> = None;
  76
  77 fn check_drops_state(num_drops: i32, last_dropped: Option<i32>) {
  78     unsafe {
  79         assert_eq!(NUM_DROPS, num_drops);
  80         assert_eq!(LAST_DROPPED, last_dropped);
  81     }
  82 }
  83
  84 struct D(i32);
  85 impl Drop for D {
  86     fn drop(&mut self) {
  87         unsafe {
  88             NUM_DROPS += 1;
  89             LAST_DROPPED = Some(self.0);
  90         }
  91     }
  92 }