Comment #0 by bearophile_hugs — 2010-03-22T07:11:14Z
This page about C#:
http://msdn.microsoft.com/en-us/library/ms173174%28VS.80%29.aspx
contains this working C# code:
class Mammals {}
class Dogs : Mammals {}
class Program {
public delegate Mammals HandlerMethod();
public static Mammals FirstHandler() { return null; }
public static Dogs SecondHandler() { return null; }
static void Main() {
HandlerMethod handler1 = FirstHandler;
HandlerMethod handler2 = SecondHandler;
}
}
This is a possible translation to D2:
class Mammals {}
class Dogs : Mammals {}
alias Mammals function() HandlerMethod;
Mammals function() handler;
Mammals FirstHandler() { return null; }
Dogs SecondHandler() { return null; }
void main() {
HandlerMethod handler1 = &FirstHandler;
HandlerMethod handler2 = &SecondHandler; // line 9, err
handler = &SecondHandler; // line 10, err
}
But the D2 code gives two compile errors:
test.d(9): Error: cannot implicitly convert expression (& SecondHandler) of type Dogs function() to Mammals function()
test.d(10): Error: cannot implicitly convert expression (& SecondHandler) of type Dogs function() to Mammals function()
It can be positive for the D type system to accept this code too.
Comment #1 by yebblies — 2011-06-08T22:48:58Z
I'm going to mark this as a dupe of 3180, along with 3833, as both cases are covered by covariance.
*** This issue has been marked as a duplicate of issue 3180 ***