void main()

{

    process!fun();

    process2!fun();

}

​

void process(alias coRoutine, T...)(T params)

{

    auto res = coRoutine(params); 

    pragma(msg, typeof(res)); 

}

​

void process2(alias coRoutine, T...)(T params)

{

    static if(T.length)

    {

        pragma(msg, typeof(coRoutine(Map!(init, T)))); 

    }

    else

    {

        pragma(msg, typeof(coRoutine())); 

    }

}

​

auto fun(T...)(T params)

{

    return 42; 

}

​

// maps a type to its init value 

private auto init(T)()

{

    return T.init;  

}

​

// ArgCall taken from https://dlang.org/library/std/meta/alias_seq.html

private auto ref ArgCall(alias Func, arg)()

{

    return Func!(arg)();

}

​

// Map taken from https://dlang.org/library/std/meta/alias_seq.html

private template Map(alias Func, args...)

{

    static if (args.length > 1)

    {

        alias Map = AliasSeq!(ArgCall!(Func, args[0]), Map!(Func, args[1 .. $]));

    }

    else

    {

        alias Map = ArgCall!(Func, args[0]);

    }

}