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|
// Copyright 2012-2013 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.
//! Miscellaneous helpers for common patterns
use cast;
use ptr;
use prelude::*;
use unstable::intrinsics;
/// The identity function.
#[inline]
pub fn id<T>(x: T) -> T { x }
/**
* Swap the values at two mutable locations of the same type, without
* deinitialising or copying either one.
*/
#[inline]
pub fn swap<T>(x: &mut T, y: &mut T) {
unsafe {
// Give ourselves some scratch space to work with
let mut tmp: T = intrinsics::uninit();
let t: *mut T = &mut tmp;
// Perform the swap, `&mut` pointers never alias
let x_raw: *mut T = x;
let y_raw: *mut T = y;
ptr::copy_nonoverlapping_memory(t, x_raw, 1);
ptr::copy_nonoverlapping_memory(x, y_raw, 1);
ptr::copy_nonoverlapping_memory(y, t, 1);
// y and t now point to the same thing, but we need to completely forget `tmp`
// because it's no longer relevant.
cast::forget(tmp);
}
}
/**
* Replace the value at a mutable location with a new one, returning the old
* value, without deinitialising or copying either one.
*/
#[inline]
pub fn replace<T>(dest: &mut T, mut src: T) -> T {
swap(dest, &mut src);
src
}
/// A non-copyable dummy type.
#[deriving(Eq, TotalEq, Ord, TotalOrd)]
#[unsafe_no_drop_flag]
pub struct NonCopyable;
impl Drop for NonCopyable {
fn drop(&mut self) { }
}
/// A type with no inhabitants
pub enum Void { }
impl Void {
/// A utility function for ignoring this uninhabited type
pub fn uninhabited(self) -> ! {
match self {
// Nothing to match on
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use clone::Clone;
use ops::Drop;
use option::{None, Some};
use mem::size_of;
#[test]
fn identity_crisis() {
// Writing a test for the identity function. How did it come to this?
let x = ~[(5, false)];
//FIXME #3387 assert!(x.eq(id(x.clone())));
let y = x.clone();
assert!(x.eq(&id(y)));
}
#[test]
fn test_swap() {
let mut x = 31337;
let mut y = 42;
swap(&mut x, &mut y);
assert_eq!(x, 42);
assert_eq!(y, 31337);
}
#[test]
fn test_replace() {
let mut x = Some(NonCopyable);
let y = replace(&mut x, None);
assert!(x.is_none());
assert!(y.is_some());
}
#[test]
fn test_noncopyable() {
assert_eq!(size_of::<NonCopyable>(), 0);
// verify that `#[unsafe_no_drop_flag]` works as intended on a zero-size struct
static mut did_run: bool = false;
struct Foo { five: int }
impl Drop for Foo {
fn drop(&mut self) {
assert_eq!(self.five, 5);
unsafe {
did_run = true;
}
}
}
{
let _a = (NonCopyable, Foo { five: 5 }, NonCopyable);
}
unsafe { assert_eq!(did_run, true); }
}
}
/// Completely miscellaneous language-construct benchmarks.
#[cfg(test)]
mod bench {
use extra::test::BenchHarness;
use option::{Some,None};
// Static/dynamic method dispatch
struct Struct {
field: int
}
trait Trait {
fn method(&self) -> int;
}
impl Trait for Struct {
fn method(&self) -> int {
self.field
}
}
#[bench]
fn trait_vtable_method_call(bh: &mut BenchHarness) {
let s = Struct { field: 10 };
let t = &s as &Trait;
bh.iter(|| {
t.method();
});
}
#[bench]
fn trait_static_method_call(bh: &mut BenchHarness) {
let s = Struct { field: 10 };
bh.iter(|| {
s.method();
});
}
// Overhead of various match forms
#[bench]
fn match_option_some(bh: &mut BenchHarness) {
let x = Some(10);
bh.iter(|| {
let _q = match x {
Some(y) => y,
None => 11
};
});
}
#[bench]
fn match_vec_pattern(bh: &mut BenchHarness) {
let x = [1,2,3,4,5,6];
bh.iter(|| {
let _q = match x {
[1,2,3,..] => 10,
_ => 11
};
});
}
}
|
