From: Sam McCall <tunah.usenet@...>
Date: 2004-08-12T23:46:12+09:00
Subject: Re: [proto-rcr] Blocks: default arguments and method signatures

David A. Black wrote:
>>That example would become:
>>
>>def transform_values(array) &block={|val,newval| out<< newval}
> 
> I can definitely see the point of the default assignment, but I
> think you're changing too much here by putting it outside the
> arglist.  &block is a special argument, I know, but it's still
> part of the list.  
That was a typo :-#

> I also don't like the forward reference to a local variable here
> (out).  When you get to this:
> 
>>	out=[] unless block_given?
> 
> it really feels a bit convoluted.  
Yes, as I posted above, I tested the equivalent code but made a mistake. 
I withdraw this part :)

>>	array.each { |value|
>>		#calculations...
>>		yield value,newvalue
> I think block.call(value,newvalue) would be clearer here, since yield
> really means that the business is being done by switching control to a
> block provided in association with the method call.  I understand that
> you're sort of retro-fitting your default block to play that role, but
> I still think it's better to save yield for the traditional yield
> scenario.
Or the block could be anonymous, which might be clear enough...

> You're not returning 'out'?
Oops, I forgot. I really couldn't test this one!

> And if you are, are you sure you want
> the return value to be nil if a block was given?
That was the intention in this example. (Recently I've been using large 
data sets, one huge array is enough!)

> Just for completeness, here's a present-day version that returns the
> original array if a block is given, and otherwise returns the
> accumulated transformations:
> 
>   def transform_values(array,&block)
>     res = if block then array else [] end
>     block ||= lambda {|val,newval| res << newval }
> 
>     array.each do |value|
>       newvalue = value * 10
>       block.call(value, newvalue)
>     end
> 
>     return res
>   end
Nice, I like the res trick...
For that matter:

def transform_values(array,&block)
    array.map{|value|
       newvalue=value*10
       block ? begin
         block[value,newvalue]; value
       end : newvalue
    }
end

Thanks,
Sam