Question

Overriding is a principle that allows you to change the functionality of a method in a child class.

For Ex.

//Overriding
public class test
{
        public virtual getStuff(int id)
        {
            //Get stuff default location
        }
}

public class test2 : test
{
        public override getStuff(int id)
        {
            //base.getStuff(id);
            //or - Get stuff new location
        }
}

When we Inherit test class in test2 at that time compiler knows that there is a virtual method in parent class.
Then why Method overring is runtime bound and not compile time bound?

Answer 1

It is run-time binding (if that is even the right phrasing – I’m not convinced) because even with a test2 variable you could actually have:

test2 obj = new test3(); // imagine test3 inherits from test2
obj.getStuff(id);

here the variable is a test2, but the object is a test3. You could argue that maybe if it was sealed etc, but actually even non-virtual instance (non-static) methods go through the callvirt process. It works well, and is very fast. Additionally, the callvirt opcode has the necessary null-check, which means your code doesn’t (under the bonnet) have to constantly check for nulls (which would be necessary if it was static-call)

The only exception here is structs which override an object method; the following is a static call:

int i = 1;
string s = i.ToString();