I am a Rust beginner and could not find anything regarding this in the docs. Would appreciate any help. The following loop in C++
for (const int i : {1,2,3,4,5})
cout << i;
roughly translates into
for &i in &[1,2,3,4,5] {
println!("{}", i);
}
Is there a way to write the equivalent of
for (int i : {1,2,3,4,5}) {
i += 1;
cout << i;
}
in Rust concisely? Namely is there a shorthand to make a local mutable copy of whats being iterated over?
Yes!
The left part of a for is a pattern.
There are three patterns that you need for this:
&pat as you already have, because you get references when iterating.mut name that creates a mutable binding. You are currently using the name pattern, which creates an immutable binding, arguably the simplest of the patterns!(pat) where parenthesis can be used to disambiguate sub-patterns.Patterns can be combined together which would give:
for &(mut i) in &[1, 2, 3, 4, 5] {
i += 1;
println!("{}", i);
}
The parenthesis are necessary to disambiguate from another pattern &mut pat which means binding a mutable reference, which isn't the same.
However, I wouldn't say this is very common, and a more common way would be to do this is two steps:
for &i in &[1, 2, 3, 4, 5] {
let i = i + 1;
println!("{}", i);
}
or
for &i in &[1, 2, 3, 4, 5] {
let mut i = i; // rebind as mutable
i += 1;
println!("{}", i);
}
&(mut i) which are not redundant. Well, at least we have #[allow(unused_parens)].