Question

Came across this code.

def setup(&block)
  @setups << block
end

What does this line do?

@setups << block

Interested in what the does “<<“.

The manual says that it is the operator of double shift, but he is here with?

Answer 1

For an array << is the append method. It adds an item to the end of the array.

So in your specific case when you call setup with a block the Proc object made from the block is stored in @setups.

Note: as sbeam points out in his comment, because << is a method, it can do different things depending on the type of object it is called on e.g. concatenation on strings, bit shifting on integers etc.

See the “ary << obj → ary” documentation.