Delegates vs. Function Pointers, part 3: C# 1.0

This is part 3 in a series about state and function pointers; part 1 is here.

Last time, we saw that it is impossible to bundle context along with a function pointer in C.

In C#, it is possible to fully achieve my standard example.  In order to explain how this works behind the scenes, I will limit this post to C# 1.0 and not use a lambda expression.  This also means no LINQ, generics, or extension methods, so I will, once again, need to write the filter method myself.

delegate bool IntFilter(int num);

static ArrayList Filter(IEnumerable source, IntFilter filter) {
    ArrayList retVal = new ArrayList();

    foreach(int i in source)
        if (filter(i))
            retVal.Add(i);
            
    return retVal;
}

class GreaterThan {
    public GreaterThan(int b) {
        this.bound = b;
    }
    int bound;
    public bool Passes(int num) {
        return num > bound;
    }
}

int x = 2;
int[] numbers = { 1, 2, 3, 4 };
Filter(numbers, new IntFilter(new GreaterThan(x).Passes));

Please excuse the ugly code; in order to be true to C# 1.0, I can’t just write an iterator, and I can’t implicitly create the delegate.

This code creates a class called GreaterThan that holds the Passes method and the state used by the method.  I create a delegate to pass to Filter out of the Passes method for an instance of the GreaterThan class from the local variable.

To understand how this works, we need to delve further into delegates.  .Net delegates are more than just type-safe function pointers. Unlike the function pointers we've looked at, delegates include state – the Target property. This property stores the object to pass as the hidden this parameter to the method (It's actually somewhat more complicated than that; I will describe open and closed delegates at a later date).  My example creates a delegate instance in which the Target property points to the GreaterThan instance.  When I call the delegate, the Passes method is called on the correct instance from the Target property, so it can read the bound field.

Next time, we'll see how the C# 2.0+ compilers generate all this boilerplate for you using anonymous methods and lambda expressions.

8 comments:

Thanks for your sharing. Hope you can contribute more quality posts to this page. Thank you!
nodejs quiz

This curiosity you describe is fantastic Rita

The above article is nice and interesting, thank you willing to share! Greetings success of admin Percetakan Murah Rawamangun Jakarta Timur wish you deign to visit my website, thank you :)

I advise you to check https://writemyessay4me.org/blog/computer-science-career out if you want to know more about computer science career. It will help you to achieve success

Thanks for the best share and i loved it,
cinema hd for windows10

Delegates vs. Function Pointers, part 3, is really great and valuable article for all the new users to developing their high interest in that but there are also some very great opportunities available like the most beneficial essay writing services which is very essential in giving their best and desirable writing services in cheap rates.

Nice post. You work very well. We provide custom boxes at wholesale rate. You can visit our site and get more information.
Custom Hair Extension Boxes Packaging UK

Beds Online: Buy Beds Online in india at best price. Shop from Customhouzz the best bed offering a wide range of king size bed, queen size bed, double bed, single bed and many more collection.

Post a Comment