为什么我需要将null合并运算符放在括号中？

Question

I have recently noticed a curiosity (at least for me). I thought that the null-coalescing operator would take the precedence over any mathematical operation but obviously i was wrong. I thought following two variables would have the same value at the end:

double? previousValue = null;
double? v1 = 1 + previousValue ?? 0;
double? v2 = 1 + (previousValue ?? 0);

But v2.Value is (the desired) 1 whereas v1.Value is still 0. Why?

Demo

Answer 1

v1 is 0 for the exact reason you mentioned: the null-coalescing operator actually has relatively low precedence. This table shows exactly how low.

So for the first expression, 1 + null is evaluated first, and it evaluates to a null int? , which then coalesces to 0.

Answer 2

v2说，1加（如果previousValue == null将值0添加到1，则给出1.V1表示1加上null为空，所以让我们给出0。