I am not sure, but perhaps all the following code should compile:


void main() {
    void function(int x) f1;
    f1 = (x) {};         // OK
    void function(ref int x) f2;
    f2 = (ref int x) {}; // OK
    f2 = (ref x) {};     // OK
    f2 = (x) {};         // Error
    void function(out int x) f3;
    f3 = (out int x) {}; // OK
    f3 = (out x) {};     // OK
    f3 = (x) {};         // Error
    void delegate(int x) d1;
    d1 = (x) {};         // OK
    void delegate(ref int x) d2;
    d2 = (ref int x) {}; // OK
    d2 = (ref x) {};     // OK
    d2 = (x) {};         // Error
    void delegate(out int x) d3;
    d3 = (out int x) {}; // OK
    d3 = (out x) {};     // OK
    d3 = (x) {};         // Error
}


DMD 2.066alpha gives:

test.d(7,10): Error: cannot implicitly convert expression (__lambda4) of type void function(int x) pure nothrow @nogc @safe to void function(ref int x)
test.d(11,10): Error: cannot implicitly convert expression (__lambda7) of type void function(int x) pure nothrow @nogc @safe to void function(out int x)
test.d(17,10): Error: cannot implicitly convert expression (__lambda11) of type void delegate(int x) pure nothrow @nogc @safe to void delegate(ref int x)
test.d(21,10): Error: cannot implicitly convert expression (__lambda14) of type void delegate(int x) pure nothrow @nogc @safe to void delegate(out int x)