Forum: IronRuby Inheritance in IronRuby - possibly a bug or two?

D2a71671c69e5bbc715d7979d69214ec?d=identicon&s=25 Charles Strahan (charles-strahan)
on 2010-09-24 09:01
(Received via mailing list)
I have a couple questions about deriving from C# class from IronRuby.
For
context, here's a code example that I will refer to here in a bit:

========================================

using System;
using System.Reflection;
using IronRuby;
using IronRuby.Runtime;
using Microsoft.Scripting.Hosting.Providers;

namespace Example1
{
    public class Person
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }

        public Person(string firstName, string lastName)
        {
            FirstName = firstName;
            LastName = lastName;
        }
    }

    class Program
    {
        private static readonly string _rubyScript = @"

class Person2 < Example1::Person
  def initialize(first, last)
    super(first, last)
  end
end

Person2.new(""Foo"", ""Bar"")

";

        static void Main(string[] args)
        {
            var runtime = Ruby.CreateRuntime();
            var engine = runtime.GetEngine("rb");
            var context =
(RubyContext)HostingHelpers.GetLanguageContext(engine);
            var scope = engine.CreateScope();
            runtime.LoadAssembly(typeof(Program).Assembly);

            engine.Execute(_rubyScript, scope);

            Console.WriteLine(". . .");
            Console.ReadKey(true);
        }
    }
}


========================================


If you run that code, you'll get the following:


InvalidOperationException: can't allocate class `Person2' that derives
from
type `Example1::Person' with no default constructor; define Person2#new
singleton method instead of Person2#initialize


Is this a bug, or is this intended behavior?  If this is intentional,
then I
think there's still a different problem: try adding this default
constructor
and then run the code:

        public Person()
        {
            Console.WriteLine("Uhmmm... what did IronRuby do with
`super(first, last)`?");
        }

So, the `super(first, last)` still get's executed... but what did it do?
It
obviously didn't forward those arguments to the non-default
constructor...

So, I think that means we have one, or possibly two, bugs.

Back to the first question: Wouldn't it be possible to determine the
correct
constructor to invoke based on the arguments, thus avoiding the
exception? I
would imagine that the generated/emitted subclass could contain all of
the
same constructors that the base type has, just passing the arguments on
to
the base class's corresponding constructor (I hope that made sense -
sorta
tricky to word that correctly).


By the way, how should I specify that I _don't_ want the Ruby code to be
interpreted? I noticed that the debugger broke
in Microsoft.Scripting.Interpreter.Interpreter... maybe that could be
part
of the problem.

Cheers,
-Charles
Cb51033949ffccd982ae32c9f890f25a?d=identicon&s=25 Tomas Matousek (Guest)
on 2010-09-24 09:43
(Received via mailing list)
This behavior is actually by design.

The error message says: "... define Person2#new singleton method instead
of Person2#initialize" like so:

class Person2 < Example1::Person
  def self.new(first, last)
    super(first, last)
  end
end

person = Person2.new("Foo", "Bar")
p person.first_name, person.last_name

We do pick up the superclass's constructors if you don't specify no
initialize method, so this works too:

class Person2 < Person
end

person = Person2.new("Foo", "Bar")
p person.first_name, person.last_name

The reason why this doesn't work when you define initialize is to make
you aware of the fact that your initialize method doesn't do what you
might expect, that is it doesn't call the constructor of the superclass.

If you define a default ctor in the superclass and you have initialize
method in the subclass, the constructor gets invoked to create the
object and initialize is called to initialize it. This patter is kind of
close to Ruby semantics.

So you basically have 3 options:

-          Do not define new nor initialize => the ctors from base class
are available for construction of the subclass

-          Define singleton new => you can choose which base ctor is
called.

-          The base class has a default ctor and the subclass defines
initialize method => the default ctor is always used for object
construction and the initialize is called with the arguments given to
"new".

The reason why we chose this design is due to difference between Ruby
and CLR initialization semantics. CLR classes don't separate allocation
("allocate") from initialization ("initialize") like Ruby does. CLR has
just constructors (which kind of corresponds to Ruby factory method
"new"). Constructors combine allocation and initialization. The problem
with mapping initialize to CLR constructors is that it operates on
"self" that is already allocated before you can do anything (like call
super):

  def initialize(first, last)
   p self.first_name                 # self is already an instance of
Person2 here, so we must have called some constructor already (the
default one if available)
    super(first, last)                   # what should this do? We can't
call the constructor again... it's too late.
  end


As for what super(first, last) does in your code ... it calls
"Object#initialize", which in Ruby 1.9.2 has *args parameters and does
nothing:

>>> class X; end
=> nil
>>> init = X.instance_method(:initialize)
=> #<UnboundMethod: X(Object)#initialize>
>>> init.parameters
=> [[:rest]]
>>> X.new.send(:initialize, 1,2,3,4,5)
=> #<X:0x0000056>

Tomas

From: ironruby-core-bounces@rubyforge.org
[mailto:ironruby-core-bounces@rubyforge.org] On Behalf Of Charles
Strahan
Sent: Thursday, September 23, 2010 11:40 PM
To: ironruby-core@rubyforge.org
Subject: [Ironruby-core] Inheritance in IronRuby - possibly a bug or
two?

I have a couple questions about deriving from C# class from IronRuby.
For context, here's a code example that I will refer to here in a bit:

========================================

using System;
using System.Reflection;
using IronRuby;
using IronRuby.Runtime;
using Microsoft.Scripting.Hosting.Providers;

namespace Example1
{
    public class Person
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }

        public Person(string firstName, string lastName)
        {
            FirstName = firstName;
            LastName = lastName;
        }
    }

    class Program
    {
        private static readonly string _rubyScript = @"

class Person2 < Example1::Person
  def initialize(first, last)
    super(first, last)
  end
end

Person2.new(""Foo"", ""Bar"")

";

        static void Main(string[] args)
        {
            var runtime = Ruby.CreateRuntime();
            var engine = runtime.GetEngine("rb");
            var context =
(RubyContext)HostingHelpers.GetLanguageContext(engine);
            var scope = engine.CreateScope();
            runtime.LoadAssembly(typeof(Program).Assembly);

            engine.Execute(_rubyScript, scope);

            Console.WriteLine(". . .");
            Console.ReadKey(true);
        }
    }
}


========================================


If you run that code, you'll get the following:

InvalidOperationException: can't allocate class `Person2' that derives
from type `Example1::Person' with no default constructor; define
Person2#new singleton method instead of Person2#initialize

Is this a bug, or is this intended behavior?  If this is intentional,
then I think there's still a different problem: try adding this default
constructor and then run the code:

        public Person()
        {
            Console.WriteLine("Uhmmm... what did IronRuby do with
`super(first, last)`?");
        }

So, the `super(first, last)` still get's executed... but what did it do?
It obviously didn't forward those arguments to the non-default
constructor...

So, I think that means we have one, or possibly two, bugs.

Back to the first question: Wouldn't it be possible to determine the
correct constructor to invoke based on the arguments, thus avoiding the
exception? I would imagine that the generated/emitted subclass could
contain all of the same constructors that the base type has, just
passing the arguments on to the base class's corresponding constructor
(I hope that made sense - sorta tricky to word that correctly).


By the way, how should I specify that I _don't_ want the Ruby code to be
interpreted? I noticed that the debugger broke in
Microsoft.Scripting.Interpreter.Interpreter... maybe that could be part
of the problem.

Cheers,
-Charles
D2a71671c69e5bbc715d7979d69214ec?d=identicon&s=25 Charles Strahan (charles-strahan)
on 2010-09-24 11:46
(Received via mailing list)
Ah, the semantics do make sense now.

In that case, perhaps there's one more solution:

class PersonShim < Example1::Person
  def self.new(first, last)
    Example1::Person.new(first, last)
  end
end

class Person2 < PersonShim
  def initialize(first, last)
    super(first, last)
  end
end

Person2.new(""Foo"", ""Bar"")



In my case, I need to make sure that the C# types that I expose to
IronRuby
behave almost identically to what you would expect with a pure Ruby
implementation. If you remember back when I was talking about my game
engine
clone, I need to make sure that I don't break user's scripts - so I need
to
preserve the "expected" semantics of `initialize`. What I could do is
end my
C# classes with "Impl", and write a corresponding Ruby class that
invokes
the correct constructor in `new` (ex: SpriteSubclass -> Sprite ->
SpriteImpl). Mind giving me a sanity check on this, Tomas?

I think this should fix the problem I was having with subclassing my
Sprite
class - which get's me one step closer to releasing this beast!


Thank you, Tomas, that was a very thorough explanation.

-Charles


On Fri, Sep 24, 2010 at 2:38 AM, Tomas Matousek <
This topic is locked and can not be replied to.