From: Daishi Harada <daishi@...>
Date: 2001-05-25T11:50:34+09:00
Subject: [ruby-talk:15689] Re: Q: Function modification/Procedures


Thanks for the reply.

I have another related question. To make a parametrized function
creator, I first tried something like:

class Adder < Proc
        def initialize(n)
                @n = n
        end
        def call(x)
                x+@n
        end
end

This broke since Proc expects a block on initialization, so you can't
just do:

add2 = Adder.new(2)

For a simple function like this I was able to instead do:

def mkadder(n); proc {|x| x+n}; end
add2 = mkadder(2)

However, for more complicated procedures it would be nice to be able
to have a real class and methods to encapsulate subprocedures into.

I currently have another potential solution as:

module Callable
        def [](x)
                call(x)
        end
end
class Adder
        include Callable
        def initialize(n)
                @n = n
        end
        def call(x)
                x+@n
        end
end

But this seems like a bit of a hack; is there a "right" way to do this
kind of thing?

Thanks again,
daishi

From: Dave Thomas <Dave@PragmaticProgrammer.com>
Subject: Re: [ruby-talk:15633] Q: Function modification/Procedures
Date: 23 May 2001 18:49:20 -0500

> You can use '[]' as an alias for call, so something like
> 
>   def some_fn(n)
>     n * 2
>   end
> 
>   def wrap(&fn)
>     proc {|x| some_fn(fn[x])}
>   end
> 
> 
>   add_3_times_2 = wrap {|x| x + 3}
> 
>   add_3_times_2[4]  #=> 14
>   add_3_times_2[-2] #=> 2
> 
> 
> I'm not sure if there's a parsing reason that you can't overload '()'.
> 
> 
> Dave
>