ruby - :& argument mean? 是什么意思

Question

我不明白此示例中注入(inject)方法的 :& 参数:

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

:+ 对我来说很有意义:

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

等同于:

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

如上例所示，:& 是什么意思？

Answer 1

Enumerable#inject

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

所以&就是Integer#&方法

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

与此相同

7 & 5 # => 5

它是如何工作的

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

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