“David Alan Black” dblack@candle.superlink.net wrote in message
news:Pine.LNX.4.30.0207131952450.9723-100000@candle.superlink.net…
Hi –
Hi all,
I am trying to add a method dynamically. I can do the following just
fine:
def create
str = “def hello (*args) puts ‘test’ end”
self.instance_eval (str)
end
This adds the hello method. But I want to pass a block to test so that
it
executes the block instead of the “puts ‘test’”.
I tried the following after searching some previous posts:
def create (&block)
str = “def hello (*args) block.call end”
self.instance_eval (str)
I believe that “self.instance_eval” is essentially the same as plain
“eval”, because instance_eval effectively sets the value of “self”,
temporarily, to its receiver – so setting it to “self” doesn’t change
anything. (Stay tuned for others pointing out possible subtleties
that I’m overlooking 
Here’s a little example of switching “self” on the fly, just for
contrast:
class Thing
def demo
puts “I am a #{type}” # => I am a Thing
s = “string”
s.instance_eval ‘puts “I am a #{type}”’ # => I am a String
end
end
end
But to be honest I don’t really know what I am doing there. 
I
realize
that instance_eval can take a block, but what name would the method be?
I’m almost, but not quite, following your description… Which
method do you mean? Could you explain a little more about the
context? I think there might be useful things you could do along the
lines of, maybe, a hash of Proc objects, or something like that, but
I’m not sure what the best fit would be.
David
–
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web: http://pirate.shu.edu/~blackdav
I am sorry, my examples were a little off. These should show it better.
Original attempt that works but without a block parameter:
def create (methodName)
str = “def " + methodName + " (*args) puts ‘test’ end”
self.instance_eval (str)
end
My attempt with a block:
def create (methodName, &block)
str = “def " + methodName + " (*args) block.call end”
self.instance_eval (str)
end
I want to call create something like this:
obj.create “newMethod” { puts “I am a new method” }
obj.create “anotherMethod” { puts “I am another method” }
and when I call newMethod it outputs the text “I am a new method”.
and when I call anotherMethod it outputs the text “I am another method”.
I could do this with a hash of proc objects like you suggested, but I would
prefer to do it using the instance_eval method as I think its cleaner (less
member variables), and I also want to learn if there is a way to associated
a block with a new method and name it.
I would also rather not pass a string for the method in to the create call.
I want to pass a block, mainly cause I want to see how to make use of the
block feature.
Make sense?
John.
···
On Sun, 14 Jul 2002, John wrote:
I realize