C# héritage, ajoutant de nouvelles méthodes - Stack Overflow

Ok so I've been searching about for a while trying to find an anwer to this question but it is difficult to phrase so I am asking here.

I'm inheriting a class like

Class A (int a, int b, int c)

public A(int a, int b, int c)
{
}

Class B : A 

public B(int a, int b, int c) base: (a, b, c)

public void blah(int something)
{

}

Why can't I do this and then do :

B classb = new B(1,2,3);

classb.blah(4);

Instead I have to do

public virtual void blah(int something)
{
}  

In class A, then in class B:

public override void blah(int something)
{
 //method to be used in B but not A.
}

So even though I have no intention of ever using the method in class A I still have to declare the virtual? So if i'm inheriting class C : B then what? I have to declare stuff in A for C?

Your assumption has no any meaning, at least as much as I understood.

Consider following example:

public class Base {}

public class Derived : Base {
    public void DerivedSpecificMethod() {
    }
}

if you do

Derived d = new Derived(); //as you specify in code example 
d.DerivedSpecificMethod(); //you CAN do this.

The virtual may be need in case when you write:

Base b = new Derived(); //note, I use a Base here on left side of equation
b.DerivedSpecificVirtualMethod(); //virtual method call

Why can't I do this and then do :

B classb = new B(1,2,3);

classb.blah(4);

You absolutely can. There's no problem with that at all, other than the syntactic errors in your code. Here's a complete example which compiles and runs with no issues. (I've fixed the naming convention violation at the same time for the blah method.)

using System;

class A
{
    public A(int a, int b, int c)
    {
    }
}

class B : A
{
    public B(int a, int b, int c) : base(a, b, c)
    {
    }

    public void Blah(int something)
    {
        Console.WriteLine("B.Blah");
    }
}



class Test
{
    static void Main()
    {
        B b = new B(1, 2, 3);
        b.Blah(10);
    }
}

There's nothing wrong with this, except that your code is not actually valid C#. I think this is what you want:

class A
{
    public A(int a, int b, int c)
    {
    }
}

class B : A 
{
    public B(int a, int b, int c) : base(a, b, c)
    {
    }

    public void blah(int something)
    {
    }
}

Then this is no problem:

B classb = new B(1,2,3);
classb.blah(4);

Your code won't compile. You don't have to use virtual specifier, this works as expected:

class App
{
    static void Main()
    {
        B classb = new B(1,2,3);
        classb.blah(4);
    }
}

class A
{
    public A(int a, int b, int c)
    {
    }
}

class B : A 
{
    public B(int a, int b, int c): base (a, b, c)
    {
    }

    public void blah(int something)
    {
        Console.WriteLine(something);
    }
}

Ok so I've been searching about for a while trying to find an anwer to this question but it is difficult to phrase so I am asking here.

I'm inheriting a class like

Class A (int a, int b, int c)

public A(int a, int b, int c)
{
}

Class B : A 

public B(int a, int b, int c) base: (a, b, c)

public void blah(int something)
{

}

Why can't I do this and then do :

B classb = new B(1,2,3);

classb.blah(4);

Instead I have to do

public virtual void blah(int something)
{
}  

In class A, then in class B:

public override void blah(int something)
{
 //method to be used in B but not A.
}

So even though I have no intention of ever using the method in class A I still have to declare the virtual? So if i'm inheriting class C : B then what? I have to declare stuff in A for C?

Your assumption has no any meaning, at least as much as I understood.

Consider following example:

public class Base {}

public class Derived : Base {
    public void DerivedSpecificMethod() {
    }
}

if you do

Derived d = new Derived(); //as you specify in code example 
d.DerivedSpecificMethod(); //you CAN do this.

The virtual may be need in case when you write:

Base b = new Derived(); //note, I use a Base here on left side of equation
b.DerivedSpecificVirtualMethod(); //virtual method call

Why can't I do this and then do :

B classb = new B(1,2,3);

classb.blah(4);

You absolutely can. There's no problem with that at all, other than the syntactic errors in your code. Here's a complete example which compiles and runs with no issues. (I've fixed the naming convention violation at the same time for the blah method.)

using System;

class A
{
    public A(int a, int b, int c)
    {
    }
}

class B : A
{
    public B(int a, int b, int c) : base(a, b, c)
    {
    }

    public void Blah(int something)
    {
        Console.WriteLine("B.Blah");
    }
}



class Test
{
    static void Main()
    {
        B b = new B(1, 2, 3);
        b.Blah(10);
    }
}

There's nothing wrong with this, except that your code is not actually valid C#. I think this is what you want:

class A
{
    public A(int a, int b, int c)
    {
    }
}

class B : A 
{
    public B(int a, int b, int c) : base(a, b, c)
    {
    }

    public void blah(int something)
    {
    }
}

Then this is no problem:

B classb = new B(1,2,3);
classb.blah(4);

Your code won't compile. You don't have to use virtual specifier, this works as expected:

class App
{
    static void Main()
    {
        B classb = new B(1,2,3);
        classb.blah(4);
    }
}

class A
{
    public A(int a, int b, int c)
    {
    }
}

class B : A 
{
    public B(int a, int b, int c): base (a, b, c)
    {
    }

    public void blah(int something)
    {
        Console.WriteLine(something);
    }
}

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