From: Martin Hart <martin@...>
Date: 2003-01-08T22:28:12+09:00
Subject: Can you detect if a method takes a block argument?

Hi all, hope everybody had a great new year - it is snowing outside for 
the first time this winter :-)

Sorry if this is common knowledge, I have done some searching of archives 
but cannot find information...
Is there a way to tell whether or not a method takes a block argument?  
The sort of thing that I want to do is write the Client class below (from 
the pseudocode example given):

class Server
	def methodWithNoBlock(arg)
		return 1
	end

	def methodWithBlock(arg, &blk)
		blk.call(1)
		blk.call(2)
	end
end

# Client is the class that I will write - sort of a delegator with knobs 
on
client = Client.new(Server.new)

# If you call the method "normally" - then everything behaves as expected
client.methodWithNoBlock => 1

# If you call the method with a block and it doesn't take a block, then 
the method's return value
# is passed as block argument. 
client.methodWithNoBlock { |arg|
	# here arg is 1, and the method returns nil
}

# If you call a method that takes a block, and you don't pass one, then 
the method's return value
# is an array of the block arguments:
client.methodWithBlock => [1, 2]

# If you call a method that takes a block, and you do pass one, then 
everything behaves as expected
client.methodWithBlock { |arg|
	# first time arg is 1, second time it is 2
	# method returns nil
}

The bit that I don't know how to do is:
1. If client detects that the requested method takes a block argument, it 
should:
 a) pass the block given to it (if there was one), or
 b) create a dummy block that fills a return array, because the caller 
didn't provide a block.

Possible? Sensible? etc.

Cheers for any help you can give,


-- 
Martin Hart              Tel:    +44 (0) 1582 618468
Arnclan                Fax:    +44 (0) 1582 619596
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