From: "W. Kent Starr" <wyzzrd@...>
Date: 2002-12-27T19:11:05+09:00
Subject: Re: viral arguments

On Fri, 2002-12-27 at 03:12, Tom Sawyer wrote:

> the idea is that rather then pass simple argumments, one could pass a little 
> piece of code that would execute in the context of the method.
> 
> here's a foo example (vproc is like proc but viral):
> 
> 	def foo(x)
> 		i = 1
> 		puts "#{x + i}"
> 	end
> 
> 	puts foo(4) --> 5
> 	puts foo(vproc {i + 1}) --> 3
> 
> any thoughts? can ruby achieve something like this already?
> 

If I am understanding you correctly,  Ruby has this mechanism already.
It is called a "block" (much better sounding than "viral" is it not?)

def foo (x=nil)
  i = 1
  x = 0 if !x   # use whatever default you want, or raise error
  return yield (i) if block_given?
  i + n
end

bar = Proc.new { |i| i + 3 }
baz = Proc.new { |i| i * 5 }

foo      #=> 1
foo 4    #=> 5
foo &bar #=> 4
foo &baz #=> 5

Thus, no argument returns a predefined default
Argument returns defined behavior operating on argument
Block returns returns operation on variable i

Note & in front of block names (bar and baz); this tells Ruby a block
has been passed (given). The block_given? method in the if statement
tests for that.

This is a very powerful feature; there are a lot of possibilities. Play
araound, experiement and enjoy.

Hope this helps?

Regards,

Kent Starr