Rust map with predicate

Question

In Rust, is there are map-like equivalent that stops iterating based on a condition I can choose?

I want to iterate over a vector, calling a function on each element as I do so and storing the results, but stop iterating if the function return value ever satisfies a condition

Iterative pseudo-code example:

results = []
for elem in vec:
    result = foo(elem)
    if result is None
        break
    results.push(result)

I can achieve a clumsy equivalent of this with scan by mutating the initial state but (AFAIK) it will still iterate over every element:

Rust-like pseudo-code for scan variant:

results = vec.iter().scan(false, |fail, elem|
    if *fail
        return None

    result = foo(elem)
    if result is None
        *fail = true
    return result
).collect()

Answer 1

results = vec.iter().map(foo).take_while(|e| e.is_some()).collect()

Iterators in Rust are lazily evaluated. In essence, the call to collect forces each element of the iterator to be evaluated one at a time. This means that as soon as some element fails the predicate in take_while, no further elements will be read from the initial iterator, let alone passed through map.