Can't understand if deallocation happens?

[Suliman via Digitalmars-d-learn]

> Supported answer: you don't, it has infinite lifetime and 
> you're claiming it is immutable, but then trying to pull the 
> memory out from under it! The supported solution is simply to 
> let the garbage collector manage it.
>
> But..
>
>>     //GC.free(str_ptr.ptr); // Error: function 
>> core.memory.GC.free (void* p) is not callable using argument 
>> types (immutable(char)*)
>
>
> If you must call the function though, you can simply 
> `cast(void*) str.ptr`, or use `char[]` up above instead of 
> `string` when declaring it, so it has a mutable pointer to 
> begin with. Since you are using .dup anyway, both declarations 
> are equally legal.

  	string str = "aaa";
  	writeln(str.length); // print 3

  	str = "bbbb";
  	writeln(str.length); //print 4 expected 3+4=7 [aaa][bbbb] (2 
blocks)
  	GC.free(cast(void*) str.ptr);
  	writeln(str.length); //print 4