TDPL: Manual invocation of destructor

[Andrei Alexandrescu]

On 08/08/2010 01:09 PM, Andrej Mitrovic wrote:
> On Page 187 it states (shortened here for convenience):
> "By calling clear(b), you invoke b's destructor, obliterate the object's state with Buffer.init, and call Buffer's default constructor"
>
> On the next page there's a unittest, and the entire example is this:
>
> import core.stdc.stdlib;
>
> class Buffer
> {
>      private void* data;
>
>      // constructor
>      this()
>      {
>          data = malloc(1024);
>      }
>
>      // destructor
>      ~this()
>      {
>          free(data);
>      }
> }
>
> unittest
> {
>      auto b = new Buffer;
>      auto b1 = b;    // extra alias for b
>      clear(b);
>      assert(b1.data is null);
> }
>
> void main() { }
>
> The assert fails, regardless if there is another reference to the object or not (b1 in this case).
>
> I've added some writeln()'s (not shown here), and just like the book said, after clear(b), b's destructor gets called, the fields get initialized to .init, and then b's constructor gets called. But the constructor will allocate memory for b1.data again, which means data is not null anymore.
>
> So I'm guessing the assert code is wrong in the example?

Yes, the assert is in error.

Andrei