From: Markus Jais <info@...>
Date: 2003-06-19T16:59:32+09:00
Subject: Re: question on blocks and iterators

>> hello
>>
>>
>> at the end is a sample code
>> this does not work as I want. I want to use each_if
>> to yield only the elements that support a certain criteria and then
>> do something with this elements. but
>> here the output is:
>>
>> ../bl.rb
>> e: 5
>> e: 8
>> e: 9
>> 2
>> 4
>> 5
>> 8
>> 9
>>
>> I do not want the numbers 2 and 4 to be printed
>>
>> I could save the elements in an array and return it but I was wondering 
if
>> there is another possibility
>
>A couple of minor changes (see comments) and this works:
>
>class Array
>
>    def each_if(b)             # no &
>        each do |e|
>            if b.call(e)
>                print "e: ", e, "\n"
>                yield e
>            end
>        end
>    end
>
>end
>
>
>a = [2, 4, 5, 8, 9]
>
>a.each_if(proc { |x| x > 4 }) { |e| puts e }
># one block above is passed as a param
>
>But you could also simply do
>
>a.select {|x| x>4 }.each {|e| puts e}
>
>Couldn't you? The print is just for debugging, right?
>
>Hal


thanks. that works fine. the print was just for debugging. I will use this 
for something else than the array class but the example was easier.

just for my understanding:
what is the difference between using "proc" as in your example and using "&" 
in the method definition like "def each_if(&b)

one thing I found is that the "&b" solution does not work because of syntax 
reasons.

../bl.rb:20: syntax error
a.each_if { |x| x > 4 } { |e| puts e }


are there any other differences ??
according to the documentation both create a Proc object.

Markus