callback function return return($var & 1)?

Question

I have read the PHP Manuel about array_filter

Answer 1

You know && is AND, but what you probably don't know is & is a bit-wise AND.

The & operator works at a bit level, it is bit-wise. You need to think in terms of the binary representations of the operands.

e.g.

710 & 210 = 1112 & 0102 = 0102 = 210

For instance, the expression $var & 1 is used to test if the least significant bit is 1 or 0, odd or even respectively.

$var & 1

010 & 110 = 0002 & 0012 = 0002 = 010 = false (even)

110 & 110 = 0012 & 0012 = 0012 = 110 = true  (odd)

210 & 110 = 0102 & 0012 = 0002 = 010 = false (even)

310 & 110 = 0112 & 0012 = 0012 = 110 = true  (odd)

410 & 210 = 1002 & 0012 = 0002 = 010 = false (even)

and so on...