mutable keyword

[Ali Çehreli via Digitalmars-d-learn]

On 05/20/2016 10:28 AM, Namespace wrote:
 > On Thursday, 19 May 2016 at 23:21:14 UTC, Jonathan M Davis wrote:
 >> On Thursday, May 19, 2016 20:44:54 ciechowoj via Digitalmars-d-learn
 >> wrote:
 >>> Is there D equivalent of C++'s mutable keyword? Like the one that
 >>> allows to modify a field of struct from constant method. Or some
 >>> alternative solution?
 >>
 >> No. D's const and immutable provide no backdoors.
 >
 > But you can cheat:
 > ----
 > int* _id;
 >
 > struct A
 > {
 >      int id = 0;
 >
 >      this(int id)
 >      {
 >          this.id = id;
 >          _id = &this.id;

Point taken but considering that D structs are freely movable value 
types, I don't think that's a valid D program. The spec does ban 
self-referencing structs but I think it also bans the code above in 
spirit. :)

 >      }
 >
 >      void change() const
 >      {
 >          (*_id)++;
 >      }
 > }
 >
 > void main() {
 >      import std.stdio;
 >
 >      A a = A(42);
 >      a.change();
 >
 >      writeln(a.id);
 > }
 > ----

Ali