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Comment by harrytuttle | Hacker News Reader

I rather prefer Java:

    void f(int n, int x) {
        Gadget p = new Gadget(n);
        // ...
        if (x < 100) throw new Exception("Weird!); // no leak
        if (x < 200) return;
        // ...
    }

Yes, good night's sleep tonight after writing that...

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The point of the example is that this is how NOT to do it in C++.

There are two better options:

  void f(int n, int x) {
      Gadget p(n); // Stack allocated
      // ...
      if (x < 100) throw new Exception("Weird!); // no leak
      if (x < 200) return;
      // ...
  }

Or, if it really has to be a pointer:

  void f(int n, int x) {
      std::unique_ptr<Gadget> p = new Gadget(n); // Smart pointer
      // ...
      if (x < 100) throw new Exception("Weird!); // no leak
      if (x < 200) return;
      // ...
  }

Both will be automatically freed as soon as the scope is exited.

What I was hoping you'd say :)

This is fine until I want to do this, at which point C++ becomes a memory management bastard:

    void f(int n, int x) {
        Gadget g = new Gadget(n);
        // ...
        if (x < 100) throw new GadgetException("Gadget broke", x);
        if (x < 200) return;
        // ...
    }

you can always fake a defer:

    void f(int n, int x) {
      Gadget g = new Gadget(n);
      std::shared_ptr<void> defer(nullptr, [g](void *) {
        delete g;
      });
    ...

But honestly ... I'd just use a stack allocated object - or a smart pointer. In the last year I didn't write one delete. (I'm a full time C++ dev).

    Gadget g = new Gadget(n);

That code won't compile unless Gadget has an assignment operator that accepts a pointer, which is, well, not a very common scenario.

Note: I'm not trying to be nitpicky. I really don't understand what you mean when you write that you "want to do this".

Now, I don't know anything about you, but based off your comments in this thread I'm not sure you have a working knowledge of C++.

Well, what's easy in Java here is that you're effectively always working with shared objects. That's easy to use, but in my experience quite error prone, I can't count how many memory leaks I fixed in Java/JS code. YMMV.

In C++, you have various ways of referencing and passing objects, so you need to be aware of the lifetime and ownership of objects. It's arguably harder, and unfortunately, the C heritage makes it a lot harder than it needs to be :(

isn't that illegal?

This code makes no sense. I think you do not understand C++ very well.

Java:

    void f(int n, int x) {
        Reader fr = new FileReader("foo.txt");
        // ...
        if (x < 100) throw new Exception("Weird!); // resource leak
        if (x < 200) return;                       // resource leak
        // ...
    }

A garbage collector that gives a false sense of security is much worse than no garbage collector at all.

try/finally in Java / using in C# are designed for that scenario.

But you'll need to document it very visibly that "Thou shalt call resource.close() whatever happened."

C++ makes it possible for the library writer to take care of freeing the resources automatically.

A class implementing IDisposable is that documentation. You shouldn't need more documentation than the fact that IDisposable is there.

An annoying fly in this ointment is cases where objects assume the responsibility for calling Dispose on caller-provided disposable objects. While it should always be okay to "double-dispose", this is only a guideline, and can't be enforced by the language, so, to maximize future compatibility with classes outside your control, you should probably defensively avoid calling Dispose on an object that will have already been disposed by other means.

And try/finally assigns the cleanup responsibility to the caller, not the callee, which just adds boilerplate and mental burden. C++ does not need a finally block due to RAII. The using block (and "try-with-resource" in Java 7) is a poor man's RAII emulation.

Anyway, what if you need to share non-memory resources? Suddenly you cannot depend on the garbage collector, you cannot use try/finally, you cannot use using or try-with-resource - you need to handle the situation just like in C++, except you're given fewer tools to do it - and a poorer understanding of the situation if you've learned that you don't need to do manual resource management due to the garbage collector.

True, but 90% of resources is memory. Java makes 90% of resources much easier to handle and 10% only little harder (like always use the try-catch-finally or try-with-resources).

They are poor solutions compared to RAII: leaky abstractions which are non-composable and error prone. Unfortunately, something like C# using is probably the best you can do in a language without clear ownership semantics like C++.

Go's defer keyword is good for this. You could also attach a finalizer to the struct, to panic/log in case it's never closed.

I'm a C# dev and I totally agree with this.

I've done a limited amount of C++ many many years ago before I even knew what garbage collection was and I keep thinking of revisiting it, but honestly in my line of work ("Enterprise") I don't need the mental overhead of dealing with things such as pointers and memory allocation.

Perhaps, my view is outdated, but I get the impression that everything in C/C++ is just a little thorny when compared to other slightly more high-level languages, such as namespaces, package management, list comprehensions, library compatibilities, type strictness etc.

I would like to be wrong about that though... I wish I had a little more motivation to spend some real time with C++ (or perhaps even C).

The point is not about C++ vs Java, it is rather about writing C++ like you would write Java, which leads to leaks.

Yes, Java is a far superior language than C++ for writing Java code.

My point entirely :)

Nitpick:

    if (x < 100) throw new Exception("Weird!); // LEAK!

You shouldn't use `new` either when throwing exceptions. Just:

    if (x < 100) throw Exception("Weird!); // no leak.

The grandparent's code is Java, not C++.

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