&str should have split_first

[SoniEx2]

string slices should have a split_first, just like array slices.

returns -> (char, &str)

[kennytm]

This function was called slice_shift_char but it was removed because you could do this instead:

fn slice_shift_char(a: &str) -> Option<(char, &str)> {
    let mut chars = a.chars();
    chars.next().map(|c| (c, chars.as_str()))
}

fn main() {
    assert_eq!(slice_shift_char("hello"), Some(('h', "ello")));
    assert_eq!(slice_shift_char("ĺḿńóṕ"), Some(('ĺ', "ḿńóṕ")));
    assert_eq!(slice_shift_char(""), None);
}

[steveklabnik]

We don't keep bugs open for small feature requests for libraries like this; big things need an RFC, small things can be PR'd. Thanks!

[Stargateur]

This function was called slice_shift_char but it was removed because you could do this instead:

fn slice_shift_char(a: &str) -> Option<(char, &str)> {
    let mut chars = a.chars();
    chars.next().map(|c| (c, chars.as_str()))
}

fn main() {
    assert_eq!(slice_shift_char("hello"), Some(('h', "ello")));
    assert_eq!(slice_shift_char("ĺḿńóṕ"), Some(('ĺ', "ḿńóṕ")));
    assert_eq!(slice_shift_char(""), None);
}

I don't feel it's a good reason. The same reasoning could be say about slice.

Also, this is far from obvious.

[kennytm]

There isn't a slice method in str

[Stargateur]

@kennytm One could say the same for slice split_first():

fn slice_shift_slice(a: &[u8]) -> Option<(u8, &[u8])> {
    let mut iter = a.iter();
    iter.next().map(|&n| (n, iter.as_slice()))
}

[kennytm]

slice::split_first has been stabilized 1.5.0. We can't retroactively destabilize a std method now even if better alternative exists.

fn split_first<T>(a: &[T]) -> Option<(&T, &[T])> {
    match a {
        [head, tail @ ..] => Some((head, tail)),
        [] => None,
    }
}

Meanwhile str::slice_shift_char was considered redundant before 1.0.0 was released, so we could remove it without the stabilization guarantee.

I was just explaining the decision made  2  5 years ago. If you would like to bring back str::split_first_char, quoting Steve above,

small things can be PR'd. Thanks!

[Stargateur]

I know all that, I just explain your argument could work the same for have refused split_first().