[Issue 3720] Taking address of member functions possible without an instance

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=3720

--- Comment #14 from Steven Schveighoffer <schveiguy at yahoo.com> ---
(In reply to Mike Franklin from comment #13)
> > My preference would be to embed in the type of the function pointer, the
> > fact that it takes a hidden context pointer. Then the compiler can disallow
> > simply calling it without stuffing it into a delegate.
> 
> Is that different from (2) in comment 11?

Yes, I would want to introduce a new piece of the type system, e.g.:

void function(this)

which means "I can only be called when in a delegate".

At the moment, we can't type the context pointer, since it's void *, and the
types will have problems if you are playing fast and loose with the delegate
internals (there is definitely code out there that plays with delegate function
pointers).

Perhaps there is room here to have loose type requirements, but I don't know
how that might break existing code. Worth exploring, though.

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