Was looking at some code in our codebase and I'm unable to understand how/why this is even working (and not causing a stackoverflow due to infinite recursion). I have pasted some equivalent code below: We have a virtual method Foo(B) defined in class P1 and overridden in class P2. P2 also defines a private non-virtual method Foo(A). B derives from A. P2::Foo(B) has a call in the end: Foo(b). I expect this to end up in a stack overflow. However, the output is: P2::Foo Virtual P2::Foo Private Non-Virtual
Looks like the second call to Foo in the overridden method is picking up the non-virtual method Foo in this case. On doing similar operations in P1 (uncomment code), we end up calling Foo infinite number of times through recursion.
Questions: (finally!) 1. Why is the behavior different in the original virtual method and the overridden method? Why is one calling itself and the other calling a different method? 2. Is there an order of preference specified somewhere? Note that if we change the private modifier to public, in both cases, we end up calling the non-virtual method (Even if we instantiate P2 this way: P1 p2 = new P2(); , instead of P2 p2 = new P2();) It looks like the non-virtual version is preferred, except when it is inside a virtual method definition. Is this true?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public class P1
{
static void Main(string[] args)
{
B b = new B();
P2 p2 = new P2();
p2.Foo(b);
// Uncomment code to cause infinite recursion
//P1 p1 = new P1();
//p1.Foo(b);
}
private void Foo(A a)
{
Console.WriteLine("P1::Foo Private Non-Virtual");
}
public virtual void Foo(B b)
{
Console.WriteLine("Inside P1::Foo");
// Uncomment code to cause infinite recursion
// Foo(b);
}
}
public class P2 : P1
{
private void Foo(A a)
{
Console.WriteLine("P2::Foo Private Non-Virtual");
}
public override void Foo(B b)
{
Console.WriteLine("P2::Foo Virtual");
Foo(b);
}
}
public class A
{
public int a = 10;
}
public class B : A
{
public int b = 20;
}
}