Is delete this allowed?

Question

Is it allowed to delete this; if the delete-statement is the last statement that will be executed on that instance of the class? Of course I'm sure that the object represented by the this-pointer is newly-created.

I'm thinking about something like this:

void SomeModule::doStuff()
{
    // in the controller, "this" object of SomeModule is the "current module"
    // now, if I want to switch over to a new Module, eg:

    controller->setWorkingModule(new OtherModule());

    // since the new "OtherModule" object will take the lead, 
    // I want to get rid of this "SomeModule" object:

    delete this;
}

Can I do this?

Answer 1

Well, in Component Object Model (COM) delete this construction can be a part of Release method that is called whenever you want to release aquisited object:

void IMyInterface::Release()
{
    --instanceCount;
    if(instanceCount == 0)
        delete this;
}

Answer 2

You can do so. However, you can't assign to this. Thus the reason you state for doing this, "I want to change the view," seems very questionable. The better method, in my opinion, would be for the object that holds the view to replace that view.

Of course, you're using RAII objects and so you don't actually need to call delete at all...right?

Answer 3

It is allowed (just do not use the object after that), but I wouldn't write such code on practice. I think that delete this should appear only in functions that called release or Release and looks like: void release() { ref--; if (ref<1) delete this; }.

Answer 4

One of the reasons that C++ was designed was to make it easy to reuse code. In general, C++ should be written so that it works whether the class is instantiated on the heap, in an array, or on the stack. "Delete this" is a very bad coding practice because it will only work if a single instance is defined on the heap; and there had better not be another delete statement, which is typically used by most developers to clean up the heap. Doing this also assumes that no maintenance programmer in the future will cure a falsely perceived memory leak by adding a delete statement.

Even if you know in advance that your current plan is to only allocate a single instance on the heap, what if some happy-go-lucky developer comes along in the future and decides to create an instance on the stack? Or, what if he cuts and pastes certain portions of the class to a new class that he intends to use on the stack? When the code reaches "delete this" it will go off and delete it, but then when the object goes out of scope, it will call the destructor. The destructor will then try to delete it again and then you are hosed. In the past, doing something like this would screw up not only the program but the operating system and the computer would need to be rebooted. In any case, this is highly NOT recommended and should almost always be avoided. I would have to be desperate, seriously plastered, or really hate the company I worked for to write code that did this.

Answer 5

The C++ FAQ Lite has a entry specifically for this

• https://isocpp.org/wiki/faq/freestore-mgmt#delete-this

I think this quote sums it up nicely

As long as you're careful, it's OK for an object to commit suicide (delete this).

Answer 6

Delete this is legal as long as object is in heap. You would need to require object to be heap only. The only way to do that is to make the destructor protected - this way delete may be called ONLY from class , so you would need a method that would ensure deletion