Ruby one liner for method undefined or nil

Question

I was curious whether there is a shorter way to check whether a method is defined on an object, and if it is, check whether it is nil or not. I've tried:

if !obj.respond_to?(:meth) || obj.meth.nil?

But it looks very long and ugly.

Answer 1

Quick and dirty but concise:

unless (obj.meth rescue nil)
  ...
end

If sending meth to obj fails (e.g. because the method is missing), the expression takes the value nil.

Of course this hides all kinds of errors in meth.

Answer 2

As @Sergio suggested, try from ActiveSupport is exactly what you want. Using try, your code would read like this:

if obj.try(:meth).nil?
  # obj either lacks :meth or has :meth that returns nil
end

Very concise and readable, I think.

If you aren't using ActiveSupport, you can quickly reimplement a simple version try yourself:

class Object
  def try(method, *args)
    public_send(method, *args) if respond_to?(method)
  end
end