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1

I'm trying to create a lambda that will return a stub class. This is what I've got:

engine_stub = lambda { |valid|
  Class.new {
    def valid?(address)
      valid
    end
  }
}

The lambda should return a class whose valid? instance method always returns the value passed to the lambda. This code fails with the error:

NameError: undefined local variable or method `valid' for #<#<Class:0x007f4bf0ebd
0f0>:0x007f4bf0ebcd08>

So clearly the method doesn't have access to the lambda scope. I also tried this:

engine_stub = lambda { |valid|
  stub_class = Class.new
  def stub_class.valid?(address)
    valid
  end
  return stub_class
}

Which instead causes this error:

NoMethodError: undefined method `valid?' for #<#<Class:0x007fecbada1138>:0x007fec
bada0df0>

So now I've failed to make valid? an instance variable.

Summary

I'm trying to get the lambda engine_stub to return a class with one instance method valid? that returns the value passed to the lambda. How do I do this?

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2 Answers

up vote 2 down vote

The keyword def is a scope gate, so you should define method via define_method{}

 engine_stub = lambda { |valid|
    Class.new do
      class << self
        define_method(:valid?) do
          valid
        end
      end
     }
   }
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up vote 0 down vote

You need to use class_eval or similar to bring value in scope.

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