What does :& argument mean?

Question

I don't understand the :&<\/code> argument for the inject method in this example:

[1, 2].map do |id|
  my_custom_method(MyModel.find(id))
end).inject(:&).map(&:category).uniq.compact.sort

Answer 1

Enumerable#inject<\/code><\/a>

If you specify a symbol instead, then each element in the collection will be passed to the named method of memo

<\/blockquote>

each bit in the result is 1 if both corresponding bits in self and other are 1, 0 otherwise