What is a pointer language?

Question

I am in the process of trying to gain a clear understanding of what a callback is. I came across this post: what-is-a-callback-function. The user 8bitjunkie who answered the question mentioned callbacks are named such because of how they are used in pointer languages. My initial assumption based on the name led me to think that a pointer language is a language where pointers can be directly manipulated. So I would like to know if c++ is a pointer language, and if my initial assumption was incorrect; what a pointer language is. As far as I can tell it does not seem to be a typical language agnostic term. If it is, it is covered by results relating to the usage of pointers.

Answer 1

Callbacks are not unique to languages that allow direct manipulation of pointers - but that is what a "Pointer Language" is. I will focus my answer on what callbacks are because that seems to be your main confusion.

Callbacks are available in Java, Python, JavaScript, and many other languages that hide pointers from you.

A callback is just a function that will be executed at the end of another function. Generally this is useful for asynchronous tasks, because it allows you to respond to the task in a specific way without blocking.

For an example I will use Java - a language with managed memory no direct access to pointers. The more native way to implement callbacks is with function pointers, and I think that is what your article meant about "Pointer Languages." But I'd rather show you what a callback is and how to use them without pointers in one fell swoop, so Java it is.

In this example we will have an interface defined like this.

public interface CallBack {
   public void onFinished(boolean success);
}

This callback interface allows us to declare an object with a predefined method that will respond to either success or failure. We can then define a Runnable class like this.

public class CBObject implements Runnable {
    private CallBack myCallback;

    public CBObject(CallBack myCallback) {
        this.myCallback = myCallback;
    }

    public void run() {
        boolean success = false;
        // do some stuff, set success = true if it works
        myCallback.onFinished(success); // this calls the callback
    }
}

Then if we want to use this callback we will do something like this.

public void doSomethingAsynchronous(CallBack callback) {
    CBObject cb = new CBObject(callback);
    Thread task = new Thread(cb);
    task.start();
}

This will run this task asynchronously but allow the user to react to its success or failure.

I hope this helps!