rust/src/libcore/util.rs

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/*!
Miscellaneous helpers for common patterns.
*/
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// NB: transitionary, de-mode-ing.
#[forbid(deprecated_mode)];
#[forbid(deprecated_pattern)];
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use cmp::Eq;
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/// The identity function.
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#[inline(always)]
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pure fn id<T>(+x: T) -> T { move x }
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/// Ignores a value.
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#[inline(always)]
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pure fn ignore<T>(+_x: T) { }
/// Sets `*ptr` to `new_value`, invokes `op()`, and then restores the
/// original value of `*ptr`.
#[inline(always)]
fn with<T: Copy, R>(
ptr: &mut T,
+new_value: T,
op: &fn() -> R) -> R
{
// NDM: if swap operator were defined somewhat differently,
// we wouldn't need to copy...
let old_value = *ptr;
*ptr = move new_value;
let result = op();
*ptr = move old_value;
return move result;
}
/**
* Swap the values at two mutable locations of the same type, without
* deinitialising or copying either one.
*/
#[inline(always)]
fn swap<T>(x: &mut T, y: &mut T) {
*x <-> *y;
}
/**
* Replace the value at a mutable location with a new one, returning the old
* value, without deinitialising or copying either one.
*/
#[inline(always)]
fn replace<T>(dest: &mut T, +src: T) -> T {
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let mut tmp <- src;
swap(dest, &mut tmp);
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move tmp
}
/// A non-copyable dummy type.
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struct NonCopyable {
i: (),
drop { }
}
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fn NonCopyable() -> NonCopyable { NonCopyable { i: () } }
mod tests {
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#[test]
fn identity_crisis() {
// Writing a test for the identity function. How did it come to this?
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let x = ~[(5, false)];
//FIXME #3387 assert x.eq(id(copy x));
let y = copy x;
assert x.eq(id(y));
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}
#[test]
fn test_swap() {
let mut x = 31337;
let mut y = 42;
swap(&mut x, &mut y);
assert x == 42;
assert y == 31337;
}
#[test]
fn test_replace() {
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let mut x = Some(NonCopyable());
let y = replace(&mut x, None);
assert x.is_none();
assert y.is_some();
}
}