virtual/override, new and not specified

Question

I get the difference between virtual/override and new modifiers. But what about times when I don't specify any modifiers.

For example I have Animal and Cat classes ( Cat inherits Animal ).

Animal class has method:

public void Say()
{
    // do something
}

And Cat class has method:

public void Say()
{
    // do something else
}

When I'm working with this methods they work as if I used new keyword.

Visual Studio shows me a warning (Use new keyword if hiding was intended).

Why does compiler won't break when I don't specify keyword. It just magically works with a little warning. Can I use some strict mode or may be edit settings in IDE.

Or may be it's a feature that I don't get :)

Answer 1

Why does compiler won't break when I don't specify keyword.

To avoid the "brittle base class" problem - where Cat originally has the Say() method, and then the author of Animal wants to add a Say() method too. With the current approach, that is not a breaking change - it will create a warning for the author of Cat , but that's all. The behaviour of all code will stay the same. The author of Cat can then decide what to do about their Say method - add the new modifier, or override Animal.Say() if that's virtual, or potentially rename the method to avoid confusion (if they control all clients as well).

Answer 2

For Animal class public virtual void Say() . For Cat public override void Say() . Then always define object of type Animal:

Animal my_cat = new Cat();
my_cat.Say();