Function generate

tutorials/external/catch.hpp:3669–3679

Note: The type after -> is weird, because VS2015 cannot parse the expression used in the typedef inside, when it is in return type. Yeah.

    //       the expression used in the typedef inside, when it is in
    //       return type. Yeah.
    auto generate( SourceLineInfo const& lineInfo, L const& generatorExpression ) -> decltype(std::declval<decltype(generatorExpression())>().get()) {
        using UnderlyingType = typename decltype(generatorExpression())::type;

        IGeneratorTracker& tracker = acquireGeneratorTracker( lineInfo );
        if (!tracker.hasGenerator()) {
            tracker.setGenerator(pf::make_unique<Generators<UnderlyingType>>(generatorExpression()));
        }

        auto const& generator = static_cast<IGenerator<UnderlyingType> const&>( *tracker.getGenerator() );
        return generator.get();
    }

} // namespace Generators
} // namespace Catch