Bitwise Or of null check in C#

Question

I was going through the IEqualityComparer Example here I don't understand the need for the second condition with Bitwise Or

if (b2 == null && b1 == null)
   return true;
else if (b1 == null | b2 == null)
   return false;

Why is there a need for such a condition?

Hovering the mouse over the pipe operator, i see a tooltip which reads "bool bool.operator|(bool left, bool right);` It appears that `bool` overloads that operator to act as a boolean or. Testing confirms that it compiles and for `bool a, b;`, `a | b` evaluates identically to `a || b`. Bonus trivia: `a ^ b` evaluates as boolean XOR, and `a & b` as boolean AND. — 15ee8f99-57ff-4f92-890c-b56153, Jun 01 '17 at 20:04
@YuriyFaktorovich I doubt that's an error, it's rarely used but its a performance boost when used properly. Seems to be the case here. — Dayan, Jun 01 '17 at 20:10
@YuriyFaktorovich in the case of two boolean values, wouldn't | produce the same results as ||? (although evaluated a little differently since || can short circuit, although I suspect | is faster in this case) — hatchet - done with SOverflow, Jun 01 '17 at 20:10
@EdPlunkett `|` and `||` do not evaluate identically. If you use `||`, `b` will not be evaluated. If you use `|`, then `b` will be evaluated. — Yuriy Faktorovich, Jun 01 '17 at 20:10
Possible duplicate of [What is the difference between the | and || or operators?](https://stackoverflow.com/questions/35301/what-is-the-difference-between-the-and-or-operators) — Dayan, Jun 01 '17 at 20:11
The answer lies here https://ericlippert.com/2015/11/02/when-would-you-use-on-a-bool/ — hatchet - done with SOverflow, Jun 01 '17 at 20:17
@hatchet I just did a not scientific test and `||` was consistently faster than `|`. — Yuriy Faktorovich, Jun 01 '17 at 20:22
@hatchet That's the accurate explanation. I ran a basic test to verify it. I hope someone upvotes your answer. — rne18145, Jun 02 '17 at 00:06

score 1 · Answer 1 · answered Jun 01 '17 at 20:04

The first condition returns true (equal) if both are null.

When you get to the second condition it's already determined that they aren't both null (or else the first condition would have been true.)

So in the second condition if either one is null then that means that only one of them is null. If one is null and the other isn't then they aren't equal.

Bitwise Or of null check in C#

1 Answers1