Vec : index of first elem satisfying property

[anon80458984]

I have:

T: Type;
v: Vec<T>;
f: Fn (&T) -> bool;

I want to get a Option<usize> of the first index i s.t. f(v[i]) returns true.

I'm looking at Vec in std::vec - Rust and there appears to be no function that returns type Option<usize>

Question: is there a builtin for solving this?

[bjorn3]

Yes:

v.iter().position(f)

Iterator in std::iter - Rust

If you want to get a reference to the element itself, you can use:

v.iter().find(f)

Iterator in std::iter - Rust

[OptimisticPeach]

You're looking for an immutable function which traverses the items in the Vec, so you should first look in the slice documentation (Because it's immutable) and then in the Iterator documentation.

my_iterator.find(f)

Should Work

my_iterator.position(f)
my_iterator.rposition(f)

Could work too.

[Yandros]

@Yandros

If you need to access the value having lead to the predicate returning true , you can use .position() to get the index of the value, or .find() to get the desired value directly.

• Note: when iterating over a str chars, you should use

.char_indices()
.find_map(|(i, c)| if predicate(c) { Some(i) } else { None })

rather than

.chars()
.position(predicate)

if intending to use the obtained number to index the str .

From Iter<Bool> -> Bool // "any" function - #3 by Yandros