TM Wrote:
> Jason House Wrote:
>
> > Steven Schveighoffer Wrote:
> >
> > >
> > > This might be a difficult thing to fix, but it definitely *definitely*
> > > needs to be fixed. The problem is that a delegate stores a function
> > > pointer and a context pointer. However, it does not type the context
> > > pointer. For example, if you do this:
> > >
> > > import std.stdio;
> > >
> > > class A
> > > {
> > > void f() const {}
> > > }
> > >
> > > void main()
> > > {
> > > const A a = new A;
> > > a.f();
> > > auto g = &a.f;
> > > writefln("%s", typeof(g).stringof);
> > > }
> > >
> > > You will get this:
> > >
> > > void delegate()
> > >
> > > The this pointer is hidden, and so is it's const decoration. I would
> > > expect to see:
> > >
> > > void delegate() const
> > >
> > > I'll file a bugzilla request for this.
> > >
> > > -Steve
> >
> >
> > I disagree. Once the delegate is passed off to some other region of code,
> > why should that other code care that there's an object that might not get
> > modified from using the delegate? Especially when you consider that which
> > object or stack frame is not tracked by the type system. Pure delegates
> > make sense to me though.
>
>
> I disagree with you. To me, the loss of the frame pointer's const attribute
> looks like a cast.
The quoted code (by Steve) above is not the same as yours. Both the variable
and the called member are const. Invoking the delegate does not violate the
const system. I did respond to your original example saying to file a bugzilla
entry.
> I do not expect to be allowed to call the above 'a.f' wihout casting a into a
> const A. And yet it is possible by using a delegate, which I think performs a
> hidden cast operation.
>
Calling a const member function is allowed without casting from either
thread-local mutable data or immutable data. Calling a non-const member
function on a const object is what's illegal. That's what your original sample
did. Constructing such a delegate (without casts) should be illegal and is a
bug in dmd.
Once a const-correct delegate is created, it should be usable like any other
delegate.
