inout, delegates, and visitor functions.

[ponce via Digitalmars-d-learn]

On Saturday, 24 October 2015 at 08:51:58 UTC, Sebastien Alaiwan 
wrote:
> Hi all,
>
> I'm trying to get the following code to work.
> (This code is a simplified version of some algebraic type).
> Is it possible to only declare one version of the 'apply' 
> function?
> Or should I declare the const version and the non-const version?
>
> I tried using "inout", but I got the following error:
>
> test.d(28): Error: inout method test.E.apply is not callable 
> using a mutable object
>
>
> class E
> {
>   void apply(void delegate(inout(E) e) f) inout
>   {
>     f(this);
>   }
>
>   int val;
> }
>
> void m()
> {
>   void setToZero(E e)
>   {
>     e.val = 0;
>   }
>
>   void printValue(const E e)
>   {
>     import std.stdio;
>     writefln("Value: %s", e.val);
>   }
>
>   E obj;
>
>   obj.apply(&setToZero);
>   obj.apply(&printValue);
> }
>
> Thanks!



Hi Sebastien,

That was an interesting question and I didn't succeed with 
'inout' either without duplicating apply.
I have a partial solution here: 
http://dpaste.dzfl.pl/b5ec7f16b912 which templatizes the delegate 
type, but is probably not what you want.

The qualifier is not carried on to the apply() function. When 
taking a const delegate it will still not be const.