C# and method hiding

Question

Per MSDN, the \"new\" keyword when used for method hiding only suppresses a warning.

http://msdn.microsoft.com/en-us/library/435f1dw2.aspx

Do I really need

Answer 1

You get method hiding whether or not you specify "new", but it's not the same as overriding. Here's an example where they're different:

using System;

class Base
{
    public virtual void OverrideMe()
    {
        Console.WriteLine("Base.OverrideMe");
    }

    public virtual void HideMe()
    {
        Console.WriteLine("Base.HideMe");
    }
}

class Derived : Base
{
    public override void OverrideMe()
    {
        Console.WriteLine("Derived.OverrideMe");
    }

    public new void HideMe()
    {
        Console.WriteLine("Derived.HideMe");
    }
}

class Test
{
    static void Main()
    {
        Base x = new Derived();
        x.OverrideMe();
        x.HideMe();
    }
}

The output is:

Derived.OverrideMe
Base.HideMe

Even though the base HideMe method is virtual, it isn't overridden in Derived, it's just hidden - so the method is still bound to the virtual method in Base, and that's what gets executed.

Member hiding is generally a bad idea, making the code harder to understand. The fact that it's available is beneficial in terms of versioning, however - it means adding a method to a base class doesn't potentially let derived classes override it unintentionally, and they can keep working as before. That's why you get the warning.