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

might help: http://en.csharp-online.net/ECMA-334%3a_14.2.1_Operator_precedence_and_associativity also http://stackoverflow.com/questions/511093/what-is-the-operator-precedence-of-c-sharp-null-coalescing-operator — Ric, Jun 28 '13 at 15:33

score 8 · Accepted Answer · answered Jun 28 '13 at 15:34

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.

score 1 · Answer 2 · answered Jun 28 '13 at 15:40

1

v2 is saying,1 plus (if previousValue == null add to 1 the value 0,which gives 1.The v1 is saying 1 plus null is null so lets give back the 0.

answered Jun 28 '13 at 15:40

terrybozzio

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

2 Answers2