In general programming, is there a way to "append to a function" and not just override the entire thing?

Question

I'm currently working with C#, and I'm using a library where you can public override void but this obviously overrides the entire method.

Is there a keyword for "appending to the method"? For example

    class A  
    {  
        public virtual void HelloWorld()  
        {  
            Console.WriteLine("Do this first");  
            Console.ReadLine();  
        }  
    }  

    class B : A  
    {  
        public append void HelloWorld() // <-- Special "append" keyword?
        {  
            Console.WriteLine("Then do this!");  
            Console.ReadLine();  
        }  
    }

So that the output of class B : A, HelloWorld() would be

Do this first
Then do this!

Normally, you'd just call the base implementation from the override. Did this not work out for you? — spender, Jun 15 '20 at 11:53
There is no such thing in C# or any programming language AFAIK. It is pointless to perform this append when you can override while still performing the base in OOP. — jegtugado, Jun 15 '20 at 11:54

score 5 · Accepted Answer · answered Jun 15 '20 at 11:57

5

You can call the parent class method by base keyword

class A
{
    public virtual void HelloWorld()
    {
        Console.WriteLine("Do this first");
    }
}

class B : A
{
    public override void HelloWorld() // <-- Special "append" keyword?
    {
        base.HelloWorld();
        Console.WriteLine("Then do this!");
    }
}

answered Jun 15 '20 at 11:57

Vivek Nuna

25,472
25
109
197

Technically this solution is OK, but be careful. Use inheritance only if you truly can my class B "is a" class A. This happens far less than you may think. In other cases you need other solutions, e.g. you may use interfaces, or just call both methods one after another etcetera. You can only inherit from one class, so take care when to use it. – RudolfJan Jun 16 '20 at 07:27

Guru Stron · Answer 2 · 2020-06-15T12:00:42.447

4

You can call base implementation in overridden method via base keyword:

class B : A
{
    public override void HelloWorld() 
    {
        base.HelloWorld(); // will print "Do this first" and wait for console input
        Console.WriteLine("Then do this!");
        Console.ReadLine();
    }
}

edited Jun 15 '20 at 12:00

answered Jun 15 '20 at 11:54

Guru Stron

102,774
10
95
132

Please code this so that it compiles without warning. – Enigmativity Jun 15 '20 at 11:59
@Enigmativity thank you, missed for some reason that. – Guru Stron Jun 15 '20 at 12:07

Shazi · Answer 3 · 2020-06-15T12:06:01.633

There is no specific keyword for what you're asking, but you can call the base implementation from the deriving class to achieve the same functionality.

class A  
{  
    public virtual void HelloWorld()  
    {  
        Console.WriteLine("Do this first");  
        Console.ReadLine();  
    }  
}  

class B : A  
{  
    public override void HelloWorld()
    {  
        base.HelloWorld();
        Console.WriteLine("Then do this!");  
        Console.ReadLine();  
    }  
}

score 1 · Answer 4 · answered Jun 15 '20 at 11:54

You need to modify your code to call the base implementation first.

class B : A  
{  
    public override void HelloWorld()
    {
        base.HelloWorld();
        Console.WriteLine("Then do this!");  
        Console.ReadLine();  
    }  
}

Language does not have any concept of this "append", nor does it require you to or provides any way to enforce that a base implementation is always called.

score 0 · Answer 5 · answered Jun 15 '20 at 11:55

0

You can use the same work in base and extra work in the child's method

class A
{
    public void DoSomething()
    {
        //Do Something
    }
}

class B: A
{
    public void DoSomethingExtra()
    {
        base.DoSomething();
        //Do extra things
    }
}

answered Jun 15 '20 at 11:55

AJITH

1,145
7
8

It wasn't my downvote, but I can tell you that it comes from the fact that OP is asking about class `A` and `B`'s methods having the **same** names/headers. Your method uses two separate names/headers. – matthew-e-brown Jun 15 '20 at 12:01
Ohh,I thought giving a meaningful name would make the context more understandable. – AJITH Jun 15 '20 at 12:26

In general programming, is there a way to "append to a function" and not just override the entire thing?

5 Answers5