From: mark sparshatt <msparshatt@...>
Date: 2004-08-07T06:27:11+09:00
Subject: Re: Defining a new function by composition

Edgardo Hames wrote:

>On Sat, 7 Aug 2004 04:46:25 +0900, Robert Klemme <bob.news@gmx.net> wrote:
>  
>
>>"Edgardo Hames" <ehames@gmail.com> schrieb im Newsbeitrag
>>news:478c16ae0408061209424c2032@mail.gmail.com...
>>    
>>
>>>I would like to add a method to the Array class, say Array#pop! which
>>>is actually split!(-1). But then, I can think of a more general
>>>problem: define a new function by composition of two or more
>>>functions.
>>>      
>>>
>>How about
>>
>>class Array
>> def pop!() split!(-1) end
>>end
>>    
>>
>
>I imagined this. But, I thought you were going to surprise me with a
>weird (or unimagined) way to use alias ;-)
>
>  
>
Though this won't do what you want since there isn't a method split! for 
array.

I think what you actually want is something like

class Array
  def pop!
    slice!(-1, 1)
  end
end

This discussion did give me an idea for a curry method, that let's you 
predefine the parameters for a method.

class Class
  def curry(newmethod, oldmethod, stored_params)
    send(:define_method, newmethod) do |*args|
      x = stored_params
      x += args if args
      send(oldmethod, *x)
    end
  end
end

then you can define pop! with

class Array
  curry(:pop!, :slice!, -1, 1)
end

then
x = [1,2,3]
p x.slice! #=> 3
p x #=> [1,2]

--
Mark Sparshatt