From: Dante Regis <dante.regis@...>
Date: 2007-10-11T11:52:55+09:00
Subject: Re: |how do you know when to put a variable between pipes?|

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My example was wrong. Where it reads

 def my_each
   my_string = ""
   i = 0
   while i <= self.size
      current_item = self[i]
      # ----
      puts current_item
      my_string += " AND #{foo}"
      # -----
   end
   self
end

it should read

 def my_each
   my_string = ""
   i = 0
   while i <= self.size
      current_item = self[i]
      # ----
      puts current_item
      my_string += " AND #{current_item}"
      # -----
   end
   self
end


On 10/10/07, Dante Regis <dante.regis@gmail.com> wrote:
>
> Another way to explain, complementing our friend Morton, is that when you
> use a block, you are kind of inserting code inside another function. Let me
> give you an example to help you understand.
>
> Let's take the "each" method of an array. You use this method when you
> want to do something with every item inside the array.
>
> You could call something like:
> my_string = ""
> my_array.each do |foo|
>   puts foo
>   my_string += " AND #{foo}"
> end
>
> Now, why did we place that |foo| on the block? Imagine that the "each"
> method on the array is implemented like this:
>
> def each
>    i = 0
>    while i <= self.size
>       current_item = self[i]
>       yield(current_item)
>    end
>    self
> end
>
> Now notice two things: First, the "each" method itself has no parameters,
> though it could have. They would have nothing to do with the pipes, though.
> Second, look at the yield line. what yield do is to call the block that you
> gave to this function. Since the yield is inside the while statement, it
> will run as many times as there are items on your array. And, as i said it
> is just like putting your piece of code inside the "each" (or any other)
> method. It would be like you've written
>
>  def my_each
>    my_string = ""
>    i = 0
>    while i <= self.size
>       current_item = self[i]
>       # ----
>       puts current_item
>       my_string += " AND #{foo}"
>       # -----
>    end
>    self
> end
>
> Now, the actual values that the block will take will clearly depend on the
> function that you are using. SInce yield can pass as many parameter as it
> wants (you could have something like yield a, b, c, d, e, ...) you should
> see the documentation of the function to know which values are passed to the
> block.
>
> It's obviously not a technical explanation, and some things are
> intentionally wrong (the each method for array is implemented in C, for
> instance), but maybe it helps you understand.
>
> Hope this helps
>

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