How to break const

[Mehrdad]

On Monday, 18 June 2012 at 14:48:37 UTC, deadalnix wrote:
> Le 18/06/2012 16:44, Mehrdad a écrit :
>> Interesting, making the delegate `pure' doesn't change 
>> anything either.
>>
>> So 'pure' doesn't let you "infer something just by looking at 
>> the code
>> either", right?
>
> It does ! It tell you that the function have no side effect, 
> and that the function called with identical arguments will 
> return identical results.
>
> pure will not ensure constness or immutability. const and 
> immutable are made for that.
>
> The fact that D decouple purity and immutability is a very nice 
> design decision and is explained nicely here : 
> http://klickverbot.at/blog/2012/05/purity-in-d/



Identical calls giving identical results? What?


import std.stdio;
struct S
{
          this(int a)
          {
                  this.a = a;
                  this.increment = { return this.a++; };
          }
          int a;
          int delegate() pure increment;
          auto oops() const { return this.increment(); }
}
void main()
{
          auto c = immutable(S)(0);
          writeln(c.oops()); // 0
          writeln(c.oops()); // 1
          writeln(c.oops()); // 2
          writeln(c.oops()); // 3
          writeln(c.oops()); // 4
          writeln(c.oops()); // 5
}