From: Robert Klemme <shortcutter@...>
Date: 2007-05-29T20:15:05+09:00
Subject: Re: Underscore

On 29.05.2007 13:07, Jano Svitok wrote:
> On 5/29/07, Jon Harrop <jon@ffconsultancy.com> wrote:
>> Michael Fellinger wrote:
>> > some people use _ as a temporary meaningless variable, just a
>> > throw-away so to say.
>> > In this case something like
>> >
>> > hash = {:a => :b, :c => :d}
>> >
>> > and you are not interested in the :b and :d
>> >
>> > hash.each do |key, _|
>> >   p key
>> > end
>> >
>> > I'm not necessarily a friend of this technique, but it seems easy on
>> > the minds of some people.
>>
>> Right, this is exactly what I guessed it was doing (it is the same in
>> SML/OCaml/F#) but what value was being thrown away in the Ruby program 
>> and
>> where did it come from?
>>
>>   (1..n).inject(x) { |acc, _| yield(acc) }
>>
>> -- 
>> Dr Jon D Harrop, Flying Frog Consultancy
>> The F#.NET Journal
>> http://www.ffconsultancy.com/products/fsharp_journal/?usenet
> 
> inject takes a block with two parameters. classic example is a sum of an 
> array:
> 
> array.inject(0) {|sum, item| sum + item }
> 
> so, in this case, item is not needed, so it is replaced by a variable
> with name of "_"
> that by convention means "temporary", "throw away"
> 
> it can be anything else:
> (1..n).inject(x) { |acc, i_dont_need_this| yield(acc) }

Actually, #inject does not really make sense in this case.  All that 
happens here is that some value is yielded n times to a block.  That 
could have been done much more concise like this:

n.times { yield x }

Kind regards

	robert