Sealed method can be overriden

Ruby IronRuby
1

Hi guys,

I’m trying to override a sealed method in IR and I succeed.

For example:
C#:
public class Shape
{
public virtual int GetNumberOfSizes() { return 0; }
}
public class Square : Shape
{
public override sealed int GetNumberOfSizes() { return 4; }
}

IR:
class NewSquare < Square
def get_number_of_sizes
return 99
end
end
puts NewSquare.new.get_number_of_sizes # => 99

Bug or by design?

Thanks,
Shay.

Shay F.
http://www.ironshay.com
Follow me: http://twitter.com/ironshay

2

You’ll be able to override anything in ruby - you’ll find CLR classes
harder
to fool.
Try creating a C# method that accepts a Shape and calls
the GetNumberOfSizes() method - I expect you’ll find that the NewSquare
override is ignored and the Square method is called instead.

I was surprised to find that a non virtual property in a C# class was
able
to be replaced by defining a new one in ruby (this was not the case for
a
non virtual method) - see

Mark.

3

Is there something special that needs to be done when overriding CLR
methods (like C#'s override keyword)?

4

In your example, you’re not overriding the sealed method (since it is
sealed :)). You’re defining a new method on the subclass. You can do
this in C# too:

class NewSquere : Square {
public new int GetNumberOfSizes() {
return 99;
}
}

As the “new” keyword suggest this method doesn’t share the v-table slot
with the base class method - it has its own new slot. Hence no virtual
call on NewSquare instance strongly typed to Shape or Square will call
your method.

Tomas

From: [email protected]
[mailto:[email protected]] On Behalf Of Mark R.
Sent: Saturday, June 13, 2009 1:37 AM
To: [email protected]
Subject: Re: [Ironruby-core] Sealed method can be overriden

You’ll be able to override anything in ruby - you’ll find CLR classes
harder to fool.

Try creating a C# method that accepts a Shape and calls the
GetNumberOfSizes() method - I expect you’ll find that the NewSquare
override is ignored and the Square method is called instead.

I was surprised to find that a non virtual property in a C# class was
able to be replaced by defining a new one in ruby (this was not the case
for a non virtual method) - see

Mark.

On Sat, Jun 13, 2009 at 6:22 PM, Shay F.
<[email protected]mailto:[email protected]> wrote:
Hi guys,

I’m trying to override a sealed method in IR and I succeed.

For example:
C#:
public class Shape
{
public virtual int GetNumberOfSizes() { return 0; }
}
public class Square : Shape
{
public override sealed int GetNumberOfSizes() { return 4; }
}

IR:
class NewSquare < Square
def get_number_of_sizes
return 99
end
end
puts NewSquare.new.get_number_of_sizes # => 99

Bug or by design?

Thanks,
Shay.

5

And also - with regular methods (not abstract, virtual sealed or
whatever), when I inherit them in IR - are the just hidden like the
static methods?

Thanks!
Shay.

Shay F.
http://www.ironshay.com
Follow me: http://twitter.com/ironshay

6

Yes, sealed virtual and “regular” methods have the same behavior.

Tomas

7

There is a slight difference though.
In the example:
puts NewSquare.new.get_number_of_sizes # => 99
puts NewSquare.new.GetNumberOfSizes # => 4

If I change the example to a regular method (not sealed), the output is
slightly different:
puts NewSquare.new.get_number_of_sizes # => 99
puts NewSquare.new.GetNumberOfSizes # => 99

Thanks,
Shay.

Shay F.
http://www.ironshay.com
Follow me: http://twitter.com/ironshay

8

No. We override the method if there is a non-sealed virtual in the base
class that has the same or un-mangled name.

Tomas

9

That’s expected. If you change “sealed override” to just “override” the
method is virtual and Ruby subclasses will override it.
In both cases NewSquare.new.GetNumberOfSizes finds CLR method
Square::GetNumberOfSizes and invokes it. In the first case, the method
is not overridden and therefore the implementation in Square gets
executed. Without “sealed” the method is overridden by
NewSquare#get_number_of_sizes and therefore the virtual dispatch
executes NewSquare’s implementation.

In both cases NewSquare.new.get_number_of_sizes finds Ruby method
NewSquare#get_number_of_sizes and executes it.

Tomas

10

The same happens with non-virtual methods as well.

By the way, should you be able to call super when you override a virtual
method?

Thanks,
Shay.

Shay F.
http://www.ironshay.com
Follow me: http://twitter.com/ironshay

11

Yes, super should work if the calling method is in a Ruby base class.

C#:
public class C {
public virtual int FooBar() { return 123; }
}

Ruby:
class D < C
def foo_bar
10 * super
end
end

p D.new.FooBar
p D.new.foo_bar

(there is a bug in the current bits that makes it throw an exception:
`get_MethodHandle’: The requested operation is invalid for
DynamicMethod. (TypeError), I’ll fix it asap).

Tomas

12

C#:
public class C {
public int FooBar() { return 123; }
}

Ruby:
require ‘x.dll’

class D < C
def foo_bar
48
end
end

p D.new.FooBar # => 123
p D.new.foo_bar # => 48

The same rules hold here: foo_bar does NOT override FooBar (since FooBar
is not virtual) and therefore is an unrelated method.
So the first call resolves to C::FooBar and invokes it.
The second call resolves to D#foo_bar and invokes it. Only if there
wasn’t foo_bar or FooBar defined in D this call would resolve to
C::FooBar.

Tomas

13

Thanks so much for the answers Tomas!

Shay F.
http://www.ironshay.com
Follow me: http://twitter.com/ironshay