From: Robert Klemme <shortcutter@...>
Date: 2011-07-05T00:54:50+09:00
Subject: Re: Are blocks objects? What messages can they handle?

On Sun, Jul 3, 2011 at 5:15 PM, Stephen Boesch <javadba@gmail.com> wrote:
> John,
>    although I was not original question author, wanted to thank you for
> that great explanation and example.

Just one point of nitpicking:

> 2011/7/3 John Feminella <johnf@bitsbuilder.com>
>
>> A block is a syntactical construct, not an object. A Proc is the
>> object-ized form of a block. If you want to do something on the block,
>> you need to turn it into an object first.
>>
>> An analogy might be that the string "def" is a syntactical construct
>> that creates a method, but it is not itself an object. You can't write
>> "def.(...)" and have it be meaningful in this context.
>>
>> > So . . . how does one send a message to the block before it is passed as
>> > an argument?  Is that even possible?
>>
>> You could make it a Proc first and pass that instead. For example, say
>> you have a method which passes some arguments to a block:
>>
>> ======
>> > def execute(*args, &block); yield *args if block; end
>>  => nil

I'd rather use these in pairs because the conversion of a block to an
accessible object has some overhead:

- block_given? and yield
- &b and b[] / b.call

So either

def execute(*args)
  yield *args if block_given?
end

or

def execute(*args, &block)
  block[*args] if block
end

respectively

def execute(*args, &block)
  block.call(*args) if block
end

Usually you only need the form with &block if you need to store the
block or pass it on to another method, e.g.

def foo
  yield 123
end

def bar(&b)
  foo(&b) # pass on
end

bar {|x| p x} # will print 123

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/