From: Mark Hubbart <discordantus@...>
Date: 2005-01-15T04:00:56+09:00
Subject: Re: Duck Typing and automated Conversions

On Fri, 14 Jan 2005 19:16:12 +0900, Robert Klemme <bob.news@gmx.net> wrote:

> def silly_example(str.to_str, count.to_int)
>   # str and count are converted like in the example above
>   s = ""
>   count.times { s << str }
>   s
> end
> 
> Basically this is just a way to save typing.  Error reporting will be the
> same.  RDoc could evaluate this info and generate comments for this
> automagically.

I could count on one hand the number of times I've converted arguments
at the top of the method. In those times, I consider it a bit of a
breakdown of duck-typing, not an extension of it.

Also, I agree with David about use of dot notation for this. This is,
in fact the reverse behavior from the usual dot notation; instead of
the expression returning the result of sending the message to the
object referenced by the variable, it references the variable to the
result of sending the message to the object.

However, I'm sure there are other alternate syntaxes that will work.
And, if you instead simply check that the passed object responds to
the selected message, that would be, imvho, an extension of
duck-typing....

  def foo( str{to_str}, count{times} )
    s = ""
    count.times { s << str }
    s
  end

If foo is called with a str that doesn't respond_to?(to_str), there
should be an error raised. Perhaps a NoMethodError, or maybe a
TypeError, or maybe something new that means both.

I'm fond of doing things like this, especially for testing, and
sometimes for working with stuff in irb:

  num, str = Object.new, Object.new

  def num.times(&block) 23.times &block end
  def str.to_str() "%02i_" % rand(99) end

  foo num, str  #==> "74_26_94_..."

I do this to make sure I'm allowing for maximum flexibility, or when
working with other's code, to find out what the actual requirements
are :)

There are a couple of problems still: First, an object might still be
able to respond to a message, using method_missing, but #respond_to?
won't show it. Second, I'm not sure about the syntax. It would work
(it currently give a parse error), but I think something better and
more self-explanatory could be found.

cheers,
Mark