c# - Why do i need to put the null-coalescing operator in brackets?

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由于您提到的确切原因是 0：空合并运算符实际上具有相对较低的优先级。该表准确显示了多低。

因此，对于第一个表达式，1 + null首先计算，然后计算为 a null int?，然后合并为 0。

Answer 2

v2 说，1 加（如果 previousValue == null 将值 0 加到 1，得到 1。v1 说 1 加 null 为空，所以让我们返回 0。