Iterating over a slice's values instead of references in Rust?
When looping over a slice of structs, the value I get is a reference (which is fine), however in some cases it's annoying to have to write var
as (*var)
in many places.
Is there a better way to avoid re-declaring the variable?
fn my_fn(slice: &[MyStruct]) {
for var in slice {
let var = *var; // <-- how to avoid this?
// Without the line above, errors in comments occur:
other_fn(var); // <-- expected struct `MyStruct`, found reference
if var != var.other {
// ^^ trait `&MyStruct: std::cmp::PartialEq<MyStruct>>` not satisfied
foo();
}
}
}
See: actual error output (more cryptic).
You can remove the reference by destructuring in the pattern:
// |
// v
for &var in slice {
other_fn(var);
}
However, this only works for Copy
-types! If you have a type that doesn't implement Copy
but does implement Clone
, you could use the cloned()
iterator adapter; see Chris Emerson's answer for more information.
In some cases you can iterate directly on values if you can consume the iterable, e.g. using Vec::into_iter()
.
With slices, you can use cloned
or copied
on the iterator:
fn main() {
let v = vec![1, 2, 3];
let slice = &v[..];
for u in slice.iter().cloned() {
let u: usize = u; // prove it's really usize, not &usize
println!("{}", u);
}
}
This relies on the item implementing Clone
or Copy
, but if it doesn't you probably do want references after all.