Pointers to non-static member functions!

[Daniel Murphy]

"Steven Schveighoffer" <schveiguy at yahoo.com> wrote in message 
news:op.vwridsuteav7ka at localhost.localdomain...
>
> Yes, but removing type safety does not prevent that from happening, plus 
> it allows something like this:
>
> class A
> {
>   void func();
>   int func2();
> }
>
> void main()
> {
>    auto a = new A;
>    auto dg = &a.func2();
>    dg.funcptr = &A.func; // works if dg.funcptr and &A.func are void*, but 
> doesn't work today
>    int x = dg(); // runs and returns garbage
> }
>
Fun fact: due to bug3797 if you change basically anything except the return 
type, it _will_ work today!

> I almost would prefer that hacking delegates would be illegal.  Yes, you 
> can get the function pointer and data pointer out of a delegate, but 
> cannot set them.  I can't think of any good use cases for them.
>

I think you're right on this.  I'll have a look and see how difficult making 
the delegate properties readonly is.  I have actually needed to manually 
construct a delegate when doing low level calling convention stuff, but you 
can always do this using unions or casts if you have to.

> I'm mixed on whether you should be able to get a member "function 
> pointer".  It would be nice to simply make it a normal function pointer 
> that you can call with the appropriate type.
>
> BTW, if the calling convention is different, we may be able to allow it 
> via creating a "this" function pointer:
>
> assert(is(typeof(&A.func2) == int function(A this)));
>
> Since this is a keyword, it can be interpreted as a different calling 
> convention.
>
> -Steve

I can see the theoretical appeal of having member function pointers or being 
able to call member functions as if they were globals, but I don't think the 
practical uses really justify introducing new syntax or types or changing 
the ABI.  I also don't think any option which does any of those things has a 
chance of getting incorporated into dmd.

If I can get some kind of consensus I'll try and patch dmd.
I think the following covers most of your points, given that you can still 
do the unsafe thing by casting:

Make delegate.funcptr read only and return void*
Make &ClassType.nonstaticmemberfunction return void*