Method overload, care to improve?


#1

Have a need to create method overloading, so I put together an
implementation. Curious what other think of it; how to improve it; or
do it a better way.

Thanks,
T.

---- overload.rb

class Module

def method_overloads
@method_overloads ||= {}
end

def overload( name, *signiture, &block )
name = name.to_sym

if method_overloads.key?( name )
  method_overloads[name][signiture] = block

else
  method_overloads[name] = {}
  method_overloads[name][signiture] = block

  if method_defined?( name )
    #method_overloads[name][nil] = instance_method( name ) #true
    alias_method( "#{name}Generic", name )
    has_generic = true
  else
    has_generic = false
  end

  define_method( name ) do |*args|
    ovr = self.class.method_overloads[:"#{name}"]
    sig = args.collect{ |a| a.class }
    hit = nil
    faces = ovr.keys.sort { |a,b| b.size <=> a.size }
    faces.each do |cmp|
      next unless cmp.size == sig.size
      cmp.size.times { |i|
        next unless cmp[i] < sig[i]
      }
      hit = cmp
    end

    if hit
      ovr[hit].call(*args)
    else
      if has_generic #ovr[nil]
        send( "#{name}Generic", *args )
        #ovr[nil].bind(self).call(*args)
      else
        raise NoMethodError
      end
    end

  end

end

end

end

_____ _

|_ |_ __| |

| |/ _ / __| __|

| | /_ \ |

||_||/__|

class X

def x
“hello”
end

overload :x, Integer do |i|
i
end

overload :x, String, String do |s1, s2|
[s1, s2]
end

end

x = X.new
p x.x
p x.x(1)
p x.x(“a”,“b”)


#2

On 20 Mar 2006 15:46:09 -0800, Trans removed_email_address@domain.invalid wrote:

Have a need to create method overloading, so I put together an

IIRC, the ‘strongtyping’ library on RAA provide method overloading
among other things.

andrew


#3

Thanks Andrew.

I’m afraid I don’t care for how the strongtyping lib handles
overloading with the #overload call internal to the method. It
undermines dynamic capabilities. Eg.

 def bar(*args)
     overload(args, String, String) {
        | s1, s2 |
        ...
        return
     }

     overload(args, String, Integer) {
        | s, i |
        ...
        return
     }

     overload_error args
  end

It would be tricky to add another overload post defnition of the
original.

T.


#4

Trans wrote:

        return

It would be tricky to add another overload post defnition of the
original.

I would agree. You loose the most powerful part - to define methods
after the
definition. One good example for multimethods are in event callbacks.
You can
capture the event you want without a bunch of switch code:

overload :mouse_down, LeftButton, ButtonDown do |button, state, x, y|
puts “left mouse button down”
end

Unfortunately it looks a bit odd. If I was using it in a library
internally it
might be cool. But exposing library users to it would be something
else. I
wonder if it could be done like this:

class Test
generic :foo

def foo.Integer_String( x, y )
return x * y
end
end

t = Test.new
t.foo( 10, 20 )

Here’s a prototype, but doesn’t quite work:

def generic( symbol )
class_eval do
#instance_variable_set( “@@#{symbol.to_s}”, Object.new )
@@foo = Object.new
define_method( symbol ) do | *args |
# Find applicable method and call
@@foo.Integer_String( *args )
end
end
end

Mike


#5

Here’s a working prototype:

class Test
#generic :foo (would generate the code below)
@@foo = Object.new
define_method :foo do |*args|
method = args.map { |a| a.class }.join( “_” )
@@foo.send( method, *args )
end
end

class Test
def @@foo.Fixnum_Fixnum( x, y )
return x * y
end

def @@foo.Fixnum_Float( x, y )
return x / y
end
end

t = Test.new
t.foo( 10, 20 )
t.foo( 10, 2.0 )

It’s inefficient and all that, but I think it looks pretty nice :slight_smile:
Mike


#6

The “methods” are executed in the context of an Object object,
instead of in the context of a Test object… And it behaves
like a singleton… And it doesn’t handle subclasses of a
Class…

No, I don’t think it’s a usable solution…

The code below would probably work better. It uses the
monitor-function “def_overload” which uses Module#wrap_method
[1] to add functionality to an already existing method. If the
arguments of a call matches the fingerprint, the given block
will be executed, otherwise the previous definition of the same
method is checked/called.

gegroet,
Erik V. - http://www.erikveen.dds.nl/

[1] http://www.erikveen.dds.nl/monitorfunctions/index.html


require “ev/metameta”

class Module
def def_overload(method, *klasses, &block)
wrap_method(method) do |org_method, args|
nok =
args.zip(klasses).find do |a, k|
if k.kind_of?(Class)
not a.kind_of?(k)
else
not a.respond_to?(k)
end
end

   if nok
     if org_method
       org_method.call(*args)
     else
       raise NotImplementedError, "Method #{self}##{method} not

implemented for arguments #{args.inspect}."
end
else
block.call(*args)
end
end
end
end

class Test
def_overload(:foo, Fixnum, :to_f) do |x, y|
x + y.to_f
end

def_overload(:foo, Fixnum, Fixnum) do |x, y|
x * y
end

def_overload(:foo, Fixnum, Float) do |x, y|
x / y
end
end

t = Test.new

p t.foo(10, 20)
p t.foo(10, 2.0)
p t.foo(10, “2”)
p t.foo(10, :two) # Should fail…


#7

Points taken for the problems of the implementation, and the metameta
solution
is nicely done. However, I would like to see if it’s possible to use
the ‘def’
syntax for defining multimethods. Below is a version I have been toying
with,
keep in mind the ‘self’ problem still exists and it is very inefficient.
Is it
possible to execute a method in a specific context, or is there a way to
make
the following work correctly?

class Generic
def find_method( args )
methods(false).sort.reverse.each do |method_name|
signature = method_name.split( “_” ).map do |i| eval i end
result = args.zip( signature ).map do |m|
m[1] == nil ? true : m[0].kind_of?( m[1] )
end
return method_name if result.inject( true ) { |a, i| a and i }
end
raise NotImplementedError
end
end

class MultimethodTest
@@foo = Generic.new

def @@foo.Fixnum( number )
puts ‘foo( Fixnum )’
end

def @@foo.String_Numeric( string, number )
puts ‘foo( String, Number )’
end

def foo( *args )
@@foo.send( @@foo.find_method( args ), *args )
end
end

t = MultimethodTest.new
t.foo( 10 )
t.foo( “Hello”, 10 )


#8

Is it possible to execute a method in a specific context,

As long as the objects are of the same class, you could use
Method#unbind and UnboundMethod#bind. If they aren’t, you could
experiment with Method#to_proc.

@@foo = Generic.new

Why?..

gegroet,
Erik V. - http://www.erikveen.dds.nl/


class Foo
def bar
self.object_id
end
end

foo1 = Foo.new
foo2 = Foo.new

p foo1.bar
p foo2.bar

p foo1.method(:bar).unbind.bind(foo2).call
p Foo.instance_method(:bar).bind(foo2).call


#9

Erik V. wrote:

Is it possible to execute a method in a specific context,

As long as the objects are of the same class, you could use
Method#unbind and UnboundMethod#bind. If they aren’t, you could
experiment with Method#to_proc.

Thanks, I’ll give it a try.

@@foo = Generic.new

Why?..

I was trying to keep the class namespace clean and to consolidate the
methods
into their own space. The unbind/bind technique is interesting - now I
tried
making the generic object the same class, and doing this:

def foo( *args )
method = @@foo.method( @@foo.find_method( args ) )
method.unbind.bind( self ).call( *args )
end

But alas, I get:
generic.rb:33:in `bind’: singleton method called for a different object
(TypeError)

I guess I don’t fully understand how singleton methods differ from
normal
methods. Thanks for all your time, this is just a curiosity not for a
project
per se.