Manufacturing methods

Ruby
1

Hi there.

Apologies if this is covered somewhere… all the googling I’ve done on
the subject has wound up with info on class-factories and and using
variables in methods. Not exactly what I’m looking for.

The question I’ve got is related to manufacturing methods. In my
particular case, I’m using a module that relies heavily on callback
methods. I need to define a couple dozen callbacks which I’d like to
all behave in basically the same way. In order to keep my code simple,
I thought I’d try manufacturing them all from the same basic code… but
haven’t found a syntax that works.

Though this syntax clearly doesn’t work, an example of the sort of thing
I’m looking for might look like this, assuming I want to create the
methods “on_foo”, “on_bar”, and “on_baz”:

%w( foo bar baz ).each do |callback|
def on_#{callback}
# callback work here
end
end

Is what I’m attempting to do even possible?

Thanks,
Matt

2

On Mon, Feb 1, 2010 at 1:05 AM, Matthew P. [email protected]
wrote:

manufacturing them all from the same basic code… but haven’t found a syntax
end

Is what I’m attempting to do even possible?

Thanks,
Matt

If you are in a class, you should can do:

class Test
%w( foo bar baz ).each do |callback|
define_method “on_#{callback}” do |param|
puts “This is method #{callback}”
puts “I have received the parameter: #{param}”
puts
end
end
end

test = Test.new
(test.methods - Object.methods).each_with_index do |method,index|
test.send method , index
end

Here is a list of useful methods like this
http://weare.buildingsky.net/2009/08/25/rubys-metaprogramming-toolbox

They are a bit cumbersome to use, though. For example, I don’t know how
to
set it up to receive a block, and you can’t use them certain places.

3

2010/2/1 Josh C. [email protected]:

I need to define a couple dozen callbacks which I’d like to all behave in
# callback work here

end

test = Test.new
(test.methods - Object.methods).each_with_index do |method,index|
test.send method , index
end

In this case there is a much simpler solution which does not need
metaprogramming:

class X
def on_event_impl(*a)
printf “args=%p\n”, a
end

alias foo on_event_impl
alias bar on_event_impl
alias baz on_event_impl
end

If you want to use a bit of metaprogramming in order to not repeat you
can do:

class Y
def on_event_impl(*a)
printf “args=%p\n”, a
end

%w{foo bar baz}.each {|m| alias_method m, :on_event_impl}
end

Yet another option is to use #method_missing

class Z
def method_missing(s, *a, &b)
if /\Aon_/ =~ s.to_s
printf “args=%p\n”, a
else
super
end
end
end

Kind regards

robert

4

Thanks very much Robert and Josh for your suggestions. It looks like
all of these work for what I need, so I’ll just need to pick one.

Thanks!
Matt