C++ mutable in D

[Dukc]

On Friday, 30 July 2021 at 19:17:55 UTC, Michael Galuza wrote:
> [snip]

We are saying that there is no direct analogue for `mutable` in 
D. It turns out we were all wrong - there is, and it even works 
in `@safe`! Behold:

```d
@safe:
alias MutableDel(T) = @safe ref T delegate();

struct Foo
{ int normalMember;
   private MutableDel!int _mutableMember;
   ref mutableMember() const {return _mutableMember();}

   this(int a, int b)
   { normalMember = a;
     _mutableMember = makeMutable(b);
   }
}

MutableDel!T makeMutable(T)(T mem) @safe
{ auto varArr = [mem];
   return ref () => varArr[0];
}


void main()
{ import std;

   const foo = Foo(5, 10);
   foo.mutableMember.writeln; //10
   foo.mutableMember = 15;
   foo.mutableMember.writeln;
}
```

Now, I definitely don't recommend using this. It might well end 
up being considered as a bug, and thus stop working in the 
future. Also the optimizer might not take this possibility into 
account, thus injecting bugs to your code.