Question

I have a code

class A < BasicObject

    def initialize var1, *args, &block
      if var1 == :lambda
        @var1 = lambda &block
      end
    end
end

a = A.new :lambda, 123  do |var|
  puts "ha ha ha"
end

why does it cause an error?

undefined method `lambda' for #<A:0x00000001687968> (NoMethodError)

unlike this one (it doesn’t cause it)

class A
   def initialize var1, *args, &block
      if var1 == :lambda
        @var1 = lambda &block
      end
    end
end

Answer 1

The lambda method is defined in the Kernel module. Object includes Kernel. BasicObject does not. So if you want to use lambda from a BasicObject, you have to call it as ::Kernel.lambda.

Note that this is not specific to lambda – it applies to any other Kernel method (like e.g. puts) as well.

PS: Note that @var1 = lambda &block does the same thing as just writing @var1 = block, so the use of lambda isn’t actually necessary here.