Function to_halfwidth

pub fn to_halfwidth(ch: char) -> Option<char>

Returns the half-width form for ch. If no half-width form for ch exists, or ch is already in half-width form, returns None.

Example

assert_eq!(unicode_hfwidth::to_halfwidth('カ'), Some('ｶ'));
assert_eq!(unicode_hfwidth::to_halfwidth('a'), None);