std.signals Can not connect a delegate without in Object

[Dsby via Digitalmars-d-learn]

import std.signals;
import std.stdio;



class hh
{
     mixin Signal!();

    void haha(){emit();}
}


class ff
{
    void show()
    {
        writeln("ff show");
    }
}

void main()
{

    auto h = new hh();

    void show()
    {
        writeln("main show");
    }

    auto f = new ff();

   // h.connect(&f.show); // It is ok to work
    h.connect(&show); // will Segmentation fault 。

    h.haha();

}