rex for method declaration

method.regex

(?x)
(?<return-type>
  (?<type-name>
    (?:
      (?:ref\s+(?:readonly\s+)?)?
      (?:
        (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\s*\:\:\s*)?
        (?<name-and-type-args>
          \g<identifier>\s*
          (?<type-args>\s*<(?:[^<>]|\g<type-args>)+>\s*)?
        )
        (?:\s*\.\s*\g<name-and-type-args>)* |
        (?<tuple>\s*\((?:[^\(\)]|\g<tuple>)+\))
      )
      (?:\s*\?\s*)?
      (?:\s*\[(?:\s*,\s*)*\]\s*)*
    )
  )\s+
)
(?<interface-name>\g<type-name>\s*\.\s*)?
(\g<identifier>)\s*
(<([^<>]+)>)?\s*
(?=\()