From: 7stud -- <bbxx789_05ss@...>
Date: 2007-11-01T06:50:41+09:00
Subject: Re: .each do |foo, bar| what does bar do?

> David A. Black wrote:
>>>> That suffers the same problem as David Black's example.
>>>
>>> What problem did mine suffer from?
>>>
>>
>> It doesn't return an array.
> 
> Was it supposed to?
> 

Hash#each returns an array(as my examples showed). You said:

>If you were going to write Hash#each in Ruby, without recourse to
>#each, 

So, yes...your example would have to return an array to implement 
Hash#each.


> If you do this:
> 
>    some_method(some_proc_object)
> 
> you're just passing the Proc object around the same way you would pass
> a string or an array or any other object.
> 
> If you do this:
> 
>    some_method &some_proc_object
> 
> you're telling some_method that you want some_proc_object to play the
> special role of code-block.
> 

Ah.  So, it's like the splat operator(*)?  With the splat operator you 
might write:

def meth1(*args)  #gathers the args into an array
  meth2(*args)    #applied a second time -- explodes the array
end

def meth2(a, b)
  p a
  p b
end

meth1(1, 2)

So, applying & a second time conceptually converts the Proc object back 
to a block and passes it to the method?


> There could even be a situation where you would do:
> 
>    some_method(proc_1, proc_2) &proc_3
> 
> i.e., send two procs as regular arguments, and use a third one as the
> code block.
> 

Whoa.  That doesn't seem consistent with your earlier example.  Why is 
proc3 outside the parentheses?  It doesn't seem to work:

def some_method(proc_1, proc_2)
  proc_1.call
  proc_2.call

  yield 'goodbye'
end

p1 = Proc.new{puts "hello"}
p2 = Proc.new{puts "world"}
p3 = Proc.new{|val| puts val}

some_method(p1, p2) &p3

--output:--
hello
world
r6test.rb:5:in `some_method': no block given (LocalJumpError)
        from r6test.rb:11


While this works:

p1 = Proc.new{puts "hello"}
p2 = Proc.new{puts "world"}
p3 = Proc.new{|val| puts val}
some_method(p1, p2, &p3)

--output:--
hello
world
goodbye
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