How to check if private method is defined in ruby

Question

The closest I can find is In Ruby, how do I check if method "foo=()" is defined?, but it only works if the method is public, even when inside the class block.

What I want:

class Foo
  private

  def bar
    "bar"
  end

  magic_private_method_defined_test_method :bar #=> true
end

What I've tried:

class Foo
  private

  def bar
    "bar"
  end

  respond_to? :bar #=> false
  #this actually calls respond_to on the class, and so respond_to :superclass gives true
  defined? :bar #=> nil
  instance_methods.include?(:bar) #=> false
  methods.include?(:bar) #=> false
  method_defined?(:bar) #=> false
  def bar
    "redefined!"
  end # redefining doesn't cause an error or anything

  public
  def bar
    "redefined publicly!"
  end #causes no error, behaves no differently whether or not #bar had been defined previously
end

Side note: I was *actually* wondering this and discovered the answer in the course of writing the question. Posted here since I couldn't easily find my answer and so I hope the next bloke will be able to. — Shelvacu, Nov 19 '15 at 21:24

score 63 · Answer 1 · edited Aug 19 '22 at 11:15

63

Another way is to use :respond_to?, e.g.

self.respond_to?(:bar, true)

Note that the second parameter is important here - it denotes that :respond_to? should look for all scope methods including private methods.

edited Aug 19 '22 at 11:15

Shelvacu

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answered Jun 16 '17 at 13:22

elquimista

2,181
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score 18 · Accepted Answer · answered Nov 19 '15 at 21:23

You want Module#private_method_defined?.

class Foo
  def do_stuff_if_bar_is_defined
    if self.class.private_method_defined?(:bar)
      do_stuff
    end
  end

  private

  def bar
    "bar"
  end

  private_method_defined? :bar #=> true
end
Foo.private_method_defined? :bar #=> true

How to check if private method is defined in ruby

2 Answers2

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