On: John Carmack discusses the art and science of soft...

[mathgladiator]

I hope he means

> if (obj != null && obj.isValid()) { }

Which is semantically correct due to the fail-fast evaluate of AND, it does require a double check since it's strange from a logic point of view. This is one the reasons that brace languages are hard to optimize since you can't commute things that ought to commute.

[astrange → mathgladiator]

That statement can't be commuted because it expresses a concept that can't be commuted.

If the two checks were independent (pure functions), it's not difficult for a compiler to determine that given enough program visibility.