Is there a builtin identity function in Rust?

Question

I have a vector of Options and I want to filter only the Somes. I use filter_map with identity:

let v = vec![Some(1), None, Some(2)];
for i in v.into_iter().filter_map(|o| o) {
    println!("{}", i);
}

Is there a builtin function permitting to write something like filter_map(identity)?

Answer 1

There is an std::convert::identity function as of Rust 1.33.0.

Answer 2

Answering your question

After Rust 1.33, see the sibling answer.

Before Rust 1.33, there is no such function in stable Rust. You can create your own:

fn id<T>(v: T) -> T { v } 

Although most people just inline the code, as you did.

Solving your problem

After Rust 1.29, use Iterator::flatten:

let v = vec![Some(1), None, Some(2)];
for i in v.into_iter().flatten() {
    println!("{}", i);
}

Before Rust 1.29, use Iterator::flat_map:

let v = vec![Some(1), None, Some(2)];
for i in v.into_iter().flat_map(|o| o) {
    println!("{}", i);
}

See also:

• Why does `Option` support `IntoIterator`?