int function() foo = { return 42; };

int delegate() bar = { return 43; };

int delegate() baz;

​

int fun(int delegate() dg) {return dg();}

​

int top_level() {return -1;}

​

Ret delegate(Args args) fun_to_dlg(Ret, Args...)(Ret function(Args args) fun)

{

    Ret delegate(Args) dlg;

    dlg.funcptr = fun;

    return dlg;

}

​

void main()

{

    assert(foo() == 42);

    assert(bar() == 43);

    assert(baz is null);

    assert(bar.ptr is null); // null frame pointer

    fun(bar);

    //fun(foo);    // cannot pass argument foo of type int function() to parameter int delegate()

    //fun(cast(int delegate())foo); // cannot cast expression foo of type int function() to int delegate()

    baz = bar;

    //baz = foo;   // cannot implicitly convert expression foo of type int function() to int delegate()

    //baz = &test; // cannot implicitly convert expression & test of type int function() to int delegate()

    baz.funcptr = &top_level;

    assert(baz.ptr is null);

    assert(baz() == -1);

    assert(fun(baz) == -1);

    //fun(&top_level); // cannot pass argument & top_level of type int function() to parameter int delegate() dg

    assert(fun(fun_to_dlg(&top_level)) == -1);

}

​

​