From: 7stud -- <bbxx789_05ss@...>
Date: 2009-03-22T12:20:55+09:00
Subject: Re: Passing a named function instead of a code block?

James Coglan wrote:
> 2009/3/20 7stud -- <bbxx789_05ss@yahoo.com>
> 
>> >> &method(:square1)
>> > grab a method as an object without calling it, we need to use
>> preceded by some symbol.
> Yes, it probably looks that way. To see the difference it helps to know 
> how
> Ruby is parsed. :square1 is an atomic unit representing the symbol whose
> name is 'square1'. ":" is not an operator, it is part of the syntax for
> symbols. However, "&" is an operator responsible for casting between 
> procs
> and blocks. The expression '&square1' should be read '&( square1 )', 
> that is
> we call square1 and cast the result of that using '&'. The same applies 
> to
> 'method'. 'method' is a method that takes a symbol/string and returns 
> the
> Method object with that name in the current scope. 'method(square1)' 
> would
> be interpreted as a call to square1, passing the result to 'method'.
> 
> So, '&square1' throws an error because you're calling a method with
> insufficient arguments. '&:square1' would try to cast a symbol to a 
> proc,
> which if you're using ActiveSupport would return the block { |object|
> object.square1 }.
> 
> '&square2' is fine as square2 is just a variable referring to a proc.
> Likewise, '&method(:square1)' is fine because method(:square1) is a 
> Method
> object, which can be cast to a block.

Thanks for the explanation.  You said that (&) casts between block and 
Procs.  But (&) also appears to be casting a Method to a block in this 
line:

puts c.collect(&method(:fib))

(&) can also be used to cast in the reverse direction, e.g. from a block 
to a Proc:

def test(&aProc)
  aProc.call(10)
end

test {|x| puts x}

--output:--
10


Can (&) cast a block to a Method?

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