I don't understand the :& 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

: makes sense to me:

[1, 2, 3].inject(: )

is the same as:

[1, 2, 3].inject { |sum, number| sum   number }

What does :& mean, as in the example above?

CodePudding user response：

Enumerable#inject

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

So & is just Integer#& method

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

[7, 5].inject(:&) # => 5

It's the same as

7 & 5 # => 5

And how it works

7.to_s(2) # => "111"
5.to_s(2) # => "101"

7: 1 1 1
   & & &
5: 1 0 1
--------
5: 1 0 1