Is it possible to introduce Automatic Reference Counting (ARC) to C++?

Question

Objective C has introduced a technology called ARC to free the developer from the burden of memory management. It sounds great, I think C++ developers would be very happy if g++

Answer 1

This is a good question. ARC is much more than just an implementation of smart pointers. It is also different from garbage collection, in that it does give you full control over memory management.

In ARC you know exactly when objects are going to be released. The reason people think is isn't true, is that there's no explicit "release" call that you write. But you know when the compiler will insert one. And it's not in some garbage collection step, it's inline when objects are considered no longer needed.

It contains a compiler step that analyzes the code and tries to find any redundant sequences of incrementing and decrementing reference counts. This could probably be achieved by an optimizing C++ compiler if it was given a smart pointer implementation that its optimizer could see through.

ARC also relies on the semantics of objective c. Firstly, pointers are annotated to say whether they are strong or weak. This could also be done in C++, just by having two different pointer classes (or using smart and vanilla pointers). Secondly, it relies on naming conventions for objective c methods to know whether their return values should be implicitly weak or strong, which means it can work alongside non-ARC code (ARC needs to know if your non-ARC code intended to return an object with a +1 reference count, for example). If your "C ARC" didn't sit alongside non-"C ARC" code you wouldn't need this.

The last thing that ARC gives you, is really good analysis of your code to say where it thinks leaks may be, at compile time. This would be difficult to add to C++ code, but could be added into the C++ compiler.