In Ruby, how do I check if method "foo=()" is defined?

Question

In Ruby, I can define a method foo=(bar):

irb(main):001:0> def foo=(bar) irb(main):002:1>   p "foo=#{bar}" irb(main):003:1> end => nil 

Now I'd like to check if it has been defined,

irb(main):004:0> defined?(foo=) SyntaxError: compile error (irb):4: syntax error, unexpected ')'  from (irb):4  from :0 

What is the proper syntax to use here? I assume there must be a way to escape "foo=" such that it is parsed and passed correctly to the defined? operator.

Answer 1

The problem is that the foo= method is designed to be used in assignments. You can use defined? in the following way to see what's going on:

defined?(self.foo=()) #=> nil defined?(self.foo = "bar") #=> nil  def foo=(bar) end  defined?(self.foo=()) #=> "assignment" defined?(self.foo = "bar") #=> "assignment" 

Compare that to:

def foo end  defined?(foo) #=> "method" 

To test if the foo= method is defined, you should use respond_to? instead:

respond_to?(:foo=) #=> false  def foo=(bar) end  respond_to?(:foo=) #=> true