Null coalescing operator, unpredictable behavior

Question

I feel confused about results of flow piece of code:

bool? _true = true;

bool? val1 = _true ?? true && false; //true
bool? val2 = (_true ?? true) && false; //false

I thought result should be the same, anyone can explain such as behavior? I noticed that it works identically at least in c# and dart so it means that should be good reason for that.

Answer 1

This is because of operator precedence, the && operation is performed before ??. So your first line is equivalent to:

bool? val1 = _true ?? (true && false);

Answer 2

The logical and operators (&&) have higher precedence than the null coalescing operator (??).

So

bool? val1 = _true ?? true && false; //true

is equal to _true ?? (true && false). Since _true is not null, the null coalescing operator returns this value (true).

In the second case

bool? val2 = (_true ?? true) && false; //false

the part in brackets is true again, but ANDed with false it results in false.

See C# operator precedence