How to print a method's parameter names

Question

Is there a quick way to output the possible parameter names of a ruby method?

For example:

def my_method(param1, param2, param3, ...) # stuff end puts get_params("my_method")

which would output something like:

param1 param2 param3 ...

Thanks!

Oh, btw I'm on ree-1.8.7...

possible duplicate of Getting Argument Names In Ruby Reflection - the original question asks slightly more, but Jorg Mittag's answer answers your question. — Andrew Grimm
– Andrew Grimm, Commented Oct 3, 2011 at 22:13
even the first response has some pretty helpful insight, thanks man — ifightcrime
– ifightcrime, Commented Oct 3, 2011 at 23:17
There's a couple of other duplicates as well: Is there a way to return a method parameter names in ruby, Reflection on method parameters in Ruby, Any ruby library to inspect what are the arguments that a certain methods take? and How do i get the names or arguments inside the method definition?. I guess it would be time to add some kind of search feature to StackOverflow, maybe a textbox in the top right corner? — Jörg W Mittag
– Jörg W Mittag, Commented Oct 4, 2011 at 0:34
Sorry, I should have edited my post earlier. I'm on ree-1.8.7 which doesn't have Method#parameters, as mentioned below. ;)I think I can get by with local_Variables, though not ideal. — ifightcrime
– ifightcrime, Commented Oct 4, 2011 at 4:07

rdvdijk · Accepted Answer · 2011-10-03 20:39:02Z

How about:

class A def my_method(param1, param2, param3) # stuff end end A.instance_method(:my_method).parameters # => [[:req, :param1],[:req, :param2],[:req, :param3]] A.instance_method(:my_method).parameters.collect { |p| p[1] } # => [:param1, param2, param3]

And if you do it on the irb console, as in your example:

>> def my_method(param1, param2, param3) >> # stuff >> end => nil >> def get_params(method_name) >> self.class.instance_method(method_name.to_sym).parameters.collect { |p| p[1] }.each { |name| puts name } >> end => nil >> get_params(:my_method) param1 param2 param3 => [:param1, :param2, :param3]

(Copy/pasted from my irb console.)

It should be know that whilst this is the best answer, Method#parameters is 1.9 only
Exactly 1.9.2. Ruby 1.9.1 doesn't contain it (at least my version ;) )
I'm stuck using ree-1.8.7, which doesn't look like it has #parameters either. This is definitely a solution though, but is there a way without that method?
+1 .. just re-read the question.. he is asking for the names of the params :)

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