Method parse

tutorials/external/catch.hpp:7452–7470

        using ParserRefImpl::ParserRefImpl;

        auto parse( std::string const &, TokenStream const &tokens ) const -> InternalParseResult override {
            auto validationResult = validate();
            if( !validationResult )
                return InternalParseResult( validationResult );

            auto remainingTokens = tokens;
            auto const &token = *remainingTokens;
            if( token.type != TokenType::Argument )
                return InternalParseResult::ok( ParseState( ParseResultType::NoMatch, remainingTokens ) );

            assert( !m_ref->isFlag() );
            auto valueRef = static_cast<detail::BoundValueRefBase*>( m_ref.get() );

            auto result = valueRef->setValue( remainingTokens->token );
            if( !result )
                return InternalParseResult( result );
            else
                return InternalParseResult::ok( ParseState( ParseResultType::Matched, ++remainingTokens ) );
        }
    };

    inline auto normaliseOpt( std::string const &optName ) -> std::string {