Le 18/06/2012 17:29, Timon Gehr a écrit :
On 06/18/2012 05:14 PM, Christophe Travert wrote:
Matthias Walter , dans le message (digitalmars.D:170036), 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.
But here, the frame pointer of the delegate is part of the const
structure. By transitivity, the frame pointer should be const, ...
'By transitivity' is not a sufficient reason. What you really mean is
'For the guarantee that a const pure method does not change its mutable
parameters'.
Transitivity by itself is required to solve a wide range of problem. The
most obvious one is controlling what is shared and what isn't using the
type system.
