Le 18/06/2012 07:59, Matthias Walter a écrit :
On 06/18/2012 07:36 AM, Mehrdad wrote:
Is it just me, or did I subvert the type system here?
import std.stdio;
struct Const
{
this(void delegate() increment)
{ this.increment = increment; }
int a;
void delegate() increment;
void oops() const { this.increment(); }
}
void main()
{
Const c;
c = Const({ c.a++; });
writeln(c.a);
c.oops();
writeln(c.a);
}
I don't think so. When calling oops you have two references to the object c:
- The this-pointer of the object itself which is not allowed to change
the object in the const-call.
- The reference from within main which is allowed to change it and can
be reached via the frame pointer of the delegate.
I see this as perfectly valid code. Of course, opinions may differ here.
Matthias
The hidden parameter of the delegate is stored in c. This hidden
parameter must be qualified with const when c is made const, for
transitivity. However, it isn't.
In short :
- c is made const
- the frame pointer is stored in c
- the frame pointer must be made const for transitivity.
=> The type system is broken. You'll find many examples of this behavior
with delegates.
