From: Robert Klemme <bob.news@...>
Date: 2005-08-09T16:46:10+09:00
Subject: Re: Proc as a parameter in a class

Simon Kr�ger wrote:
> Yannick Turgeon wrote:
>
>> Hello all,
>>
>> I'm currently playing with proc and code block as parameter trying to
>> learn this aspect. Bellow is some code: three sections. The first one
>> explain by itself what I whant to do, except that I would like to use
>> classes. The second is the same in my point of view than the first
>> one and using a class... but it's now doing what I was expecting.
>> The third one is working but I don' understand why it should be like
>> this. Anybody can give me the reason?
>>
>> Thanks.
>>
>> Yannick
>>
>> ---------------------------------
>> ##### FIRST SECTION #####
>> puts "First section"
>>
>> def fn(text)
>>     return proc{|factor| puts text * factor}
>> end
>>
>> f = fn("Joe ")
>> f.call(3)       #It prints "Joe Joe Joe ", as expected.
>>
>>
>>
>>
>> ##### SECOND SECTION #####
>> puts "Second section"
>>
>> class Bob
>>     def initialize(factor, &block)
>>         @factor = factor
>>         @action = block
>>     end
>>
>>     def run
>>         @action.call(@factor)
>>     end
>> end
>>
>> b = Bob.new(3){f}
>> b.run         #It prints nothing [b.run return the function returned
>> by fn()]
>>
>>
>>
>> ##### THIRD SECTION #####
>> puts "Third section"
>>
>> #Redefine run()
>> class Bob
>>     def run
>>         @action.call.call(@factor)      #Why should I call "call"
>> twice. Isn't @action supposed to be the function returned by fn()?
>>     end
>> end
>>
>> b = Bob.new(3){f}
>> b.run()         #It prints "Joe Joe Joe ".
>> ---------------------------------
>>
>>
>>
>
> @action is the block.
> @action.call excutes the block which returns f
> f.call prints "Joe Joe Joe "
>
> cheers
>
> Simon

Here's another variant: the proc is reconverted to a block:

##### SECOND SECTION #####
puts "Second section"

class Bob
    def initialize(factor, &block)
        @factor = factor
        @action = block
    end

    def run
        @action.call(@factor)
    end
end

# note the end of next line
b = Bob.new(3, &f)
b.run         #It prints nothing [b.run return the function returned by
fn()]

Kind regards

    robert