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up vote 1 down vote favorite

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
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2 Answers

up vote 6 down vote accepted

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.

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1  
what should I do to use lambda then? –  Marius Kavansky Jan 11 at 22:19
 
@AlanDert I've expanded my answer. –  sepp2k Jan 11 at 22:20
 
uninitialized constant Kernel (NameError) –  Marius Kavansky Jan 11 at 22:22
 
@AlanDert Ah, sorry, my bad. ::Kernel then. –  sepp2k Jan 11 at 22:23
 
Note that @var1 = lambda &block does the same thing as just writing @var1 = block Can you please give a link where it's explained? I already ready about blocks, lambdas, proc and there was no information about it. –  Marius Kavansky Jan 11 at 22:35
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up vote 0 down vote

You are using BasicObject as base class which is an explicit Blank class and specifically does not include Kernel, so you need the qualifier ::Kernel when you access any Kernel method.

On a separate note -

Instead of passing an argument that you have a block you can use the Kernel method block_given? So taking your example - 

class A
  def initialize  *args, &block
    if block_given?
      @var1 = lambda &block
    end
    puts @var1.call
  end
end
a = A.new  123  do |var|
  puts "ha ha ha"
end
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