Description
The methods at and name on Captures<'t> return "" to represent both failed matches and successful matches against the empty string. In the case of at, a programmer can use pos to distinguish between the two situations. But in the case of name, there's no good, public API which allows us to test for a match.
The follow regex has two named matched groups, key and value. value is optional:
// Matches "foo", "foo;v=bar" and "foo;v=".
regex!(r"(?P<key>[a-z]+)(;v=(?P<value>[a-z]*))?");We can access value using caps.name("value"), but there's no way for us to distinguish between the "foo" and "foo;v=" cases.
Even if we're willing to treat both meanings of "" as "failed match", it's still a nuisance to convert them to Option:
fn name<'t>(caps: &Captures<'t>, name: &str) -> Option<&'t str> {
let s = caps.name(name);
if s == "" { None } else { Some(s) }
}Now, I don't know whether it would be better to modify at and name to return Option, or add new at_opt and name_opt functions. But at the very least, there should be some convenient way to distinguish between the cases "foo" and "foo;v=".
This would be relatively easy to implement, because Captures uses Option internally.