E4209

Compiler diagnostic name: duplicate_regex_match_binding.

Duplicate regex match binding.

Each special binding in a regex match expression can be specified at most once. Using before or after multiple times would give the same part of the match more than one name.

Erroneous example

fn match_text(s : String) -> Unit {
  ignore(s =~ (re"a", before=head, before=prefix))
}

Suggestion

Use each binding label only once.

fn match_text(s : String) -> Unit {
  ignore(s =~ (re"a", before=head, after=tail))
}