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History variables: Difference between revisions
Added Rust
(Added Rust) |
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Line 2,127:
p foo_hist # => ["banana", "pear", "apple"]
</lang>
=={{header|Rust}}==
<lang Rust>#[derive(Clone, Debug)]
struct HVar<T> {
history: Vec<T>,
current: T,
}
impl<T> HVar<T> {
fn new(val: T) -> Self {
HVar {
history: Vec::new(),
current: val,
}
}
fn get(&self) -> &T {
&self.current
}
fn set(&mut self, val: T) {
self.history.push(std::mem::replace(&mut self.current, val));
}
fn history(&self) -> (&[T], &T) {
(&self.history, &self.current)
}
fn revert(&mut self) -> Option<T> {
self.history
.pop()
.map(|val| std::mem::replace(&mut self.current, val))
}
}
fn main() {
let mut var = HVar::new(0);
var.set(1);
var.set(2);
println!("{:?}", var.history());
println!("{:?}", var.revert());
println!("{:?}", var.revert());
println!("{:?}", var.revert());
println!("{:?}", var.get());
}</lang>
{{out}}
<pre>([0, 1], 2)
Some(2)
Some(1)
None
0</pre>
=={{header|Scala}}==
Scala doesn't have a native support for history variables, but it's quite easy to implement them. The following class uses same conventions as ML's mutable reference cells. (i.e. <code>!</code> as accessor, and <code>:=</code> as mutator.)
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