Question

I want to use the combination method with a custom class.

If my class looks like this…

class MyClass
  def initialize
    @data = []
  end
  def to_a
    @data
  end
end

I could call this…

myobj = MyClass.new
myobj.to_a.combination(2) {|a,b| puts "#{a} #{b}" }

But I’d much rather have this…

myobj.combination {|a,b| puts "#{a} #{b}" }

I’ve tried to write a class method to wrap the combination method, passing the block. But it’s not working.

def combination(&block)
  @data.to_a.combination(2) block.call
end

Also, does anyone know why combination is in the Array class and not Enumerable? I’d have thought it would have been more useful there.

Answer 1

The block is a special type of parameter to Array#combination (much like you’ve got it in your own definition). The correct invocation is:

def combination(&block)
  @data.to_a.combination(2, &block)
end