121 lines
2.6 KiB
Rust
121 lines
2.6 KiB
Rust
/*!
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Miscellaneous helpers for common patterns.
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*/
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// NB: transitionary, de-mode-ing.
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#[forbid(deprecated_mode)];
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#[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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pub 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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pub pure fn ignore<T>(_x: T) { }
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/// Sets `*ptr` to `new_value`, invokes `op()`, and then restores the
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/// original value of `*ptr`.
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#[inline(always)]
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pub fn with<T: Copy, R>(
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ptr: &mut T,
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new_value: T,
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op: &fn() -> R) -> R
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{
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// NDM: if swap operator were defined somewhat differently,
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// we wouldn't need to copy...
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let old_value = *ptr;
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*ptr = move new_value;
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let result = op();
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*ptr = move old_value;
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return move result;
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}
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/**
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* Swap the values at two mutable locations of the same type, without
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* deinitialising or copying either one.
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*/
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#[inline(always)]
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pub fn swap<T>(x: &mut T, y: &mut T) {
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*x <-> *y;
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}
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/**
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* Replace the value at a mutable location with a new one, returning the old
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* value, without deinitialising or copying either one.
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*/
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#[inline(always)]
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pub fn replace<T>(dest: &mut T, src: T) -> T {
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let mut tmp = move src;
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swap(dest, &mut tmp);
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move tmp
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}
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/// A non-copyable dummy type.
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pub struct NonCopyable {
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i: (),
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drop { }
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}
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pub fn NonCopyable() -> NonCopyable { NonCopyable { i: () } }
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/**
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A utility function for indicating unreachable code. It will fail if
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executed. This is occasionally useful to put after loops that never
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terminate normally, but instead directly return from a function.
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# Example
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~~~
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fn choose_weighted_item(v: &[Item]) -> Item {
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assert v.is_not_empty();
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let mut so_far = 0u;
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for v.each |item| {
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so_far += item.weight;
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if so_far > 100 {
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return item;
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}
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}
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// The above loop always returns, so we must hint to the
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// type checker that it isn't possible to get down here
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util::unreachable();
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}
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~~~
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*/
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pub fn unreachable() -> ! {
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fail ~"internal error: entered unreachable code";
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}
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mod tests {
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#[legacy_exports];
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#[test]
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fn identity_crisis() {
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// Writing a test for the identity function. How did it come to this?
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let x = ~[(5, false)];
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//FIXME #3387 assert x.eq(id(copy x));
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let y = copy x;
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assert x.eq(&id(move y));
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}
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#[test]
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fn test_swap() {
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let mut x = 31337;
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let mut y = 42;
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swap(&mut x, &mut y);
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assert x == 42;
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assert y == 31337;
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}
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#[test]
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fn test_replace() {
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let mut x = Some(NonCopyable());
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let y = replace(&mut x, None);
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assert x.is_none();
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assert y.is_some();
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}
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}
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