Dynamically adding methods to a Ruby class

Ruby
1

I just finished writing the first spike for my Ruby CLR bridge tonight,
and
I’m wondering if there might be a better (or more efficient) way to add
instance methods to a class object than this:

class Module
def const_missing(symbol)
obj = Class.new
obj.class_eval %{
def initialize
…
end

  def method_missing(name, *params)
           ...
  end
}
const_set(symbol, obj)

end
end

Thanks,
-John

PS If you’re wondering what the code in the … blocks do, read my
write-up
of this code at:
http://www.iunknown.com/articles/2005/12/14/hello-rubyclr

2

John L. wrote:

I just finished writing the first spike for my Ruby CLR bridge tonight,
and
I’m wondering if there might be a better (or more efficient) way to add
instance methods to a class object than this:

class Module
def const_missing(symbol)
obj = Class.new
obj.class_eval %{
def initialize
…
end

  def method_missing(name, *params)
           ...
  end
}
const_set(symbol, obj)

end
end

Not really, except for using define_method (which has
some limitations that would probably make it unsuitable
for a #method_missing implementation). The ‘Class methods’
thread had pretty much this exact implementation…

Perhaps some sort of a prototype-based approach?

Thanks,
-John
http://www.iunknown.com

PS If you’re wondering what the code in the … blocks do, read my
write-up
of this code at:
http://www.iunknown.com/articles/2005/12/14/hello-rubyclr

E

3

Hello John,

This isn’t quite as cool as a prototype, but here is another possible
type
of solution:

class Dynamic
attr_reader :dynamic_methods

def initialize
    @dynamic_methods = Hash.new
end

alias alias_method_missing method_missing

def method_missing(name, *args)
    unless @dynamic_methods.include?(name)
        alias_method_missing(name, *args)
        return
    end

    @dynamic_methods[name].call(*args)
end

end

d = Dynamic.new

You can also use Proc.new instead of lambda

d.dynamic_methods[:test] = lambda do |*args|
puts 'test ’ + args.to_s
end

d.test(1, 2)

test 12

Of course you could add the method that you describe in your link:

d.dynamic_methods[:Count] = lambda do |*args|
create_ruby_instance_method(self.class, ‘Count’) do
include ‘System.Collections’
ldarg_2
call ‘static Marshal::ToClrObject(VALUE)’
call ‘ArrayList::get_Count()’
call ‘static Marshal::ToRubyNumber(Int32)’
ret
end
self.Count
end

–
Brian T.
http://freeopinion.org

4

John L. wrote:

  end

  def method_missing(name, *params)
           ...
  end
}
const_set(symbol, obj)

end
end

class Module
def const_missing(symbol)
obj = Class.new do
def initialize
…
end

  def method_missing(name, *params)
           ...
  end
end
const_set(symbol, obj)

end
end

Note that this might have adversary effects on other code if consts
spring
into existence just like that.

Kind regards

robert
5

On 12/15/05, Robert K. [email protected] wrote:

Note that this might have adversary effects on other code if consts spring
into existence just like that.

I trimmed most of the code out of that example for clarity, but there
will
be a bunch of code that will looks up valid types to instantiate and
will
punt to an old_method_missing call if the constant name is an invalid
type.

Thanks for the constructor block suggestion - I did have a version
sometime
last night that used that feature, but I can’t recall why I changed it.

Cheers,
-John

6

Oops…
In the :Count method I defined, self isn’t the same as in the method you
defined.

caller[1] probably would be the object you are looking for as long as
that
method gets called through :method_missing in this case. :self could be
used
if the dynamic method is defined in the class though.

d.dynamic_methods[:Count] = lambda do |*args|
create_ruby_instance_method(caller[1].class, ‘Count’) do
include ‘System.Collections’
ldarg_2
call ‘static Marshal::ToClrObject(VALUE)’
call ‘ArrayList::get_Count()’
call ‘static Marshal::ToRubyNumber(Int32)’
ret
end
caller[1].Count
end

–
Brian T.
http://freeopinion.org

7

Thanks for the suggestion, Brian.

The code in method_missing will use reflection to generate the shim on
the
fly, so I don’t need to keep a list of methods that have been generated.
The
shim is added as an instance method to the class object, so subsequent
calls
will always go via the shim and not via method_missing.

Cheers,
-John