How to break const

[Mehrdad]

On Monday, 18 June 2012 at 06:00:11 UTC, Matthias Walter wrote:
> 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



My trouble isn't with the delegate, it's with the const method.

It's with the idea that "you can tell something about the code 
just by looking at it".

The way I understood it, you can assume that a `const` method 
cannot modify an object, but... that doesn't seem to be the case 
here.

What am I misunderstanding?