or how the simple things trip you up
I was writing a quick bit of code to add two nullable integers. To cope with the null, I used the wonderfully simple null coalescing operator ?? in C# to convert the integers to zero, like this:
int result = a ?? 0 + b ?? 0;
The result was wrong as demonstrated below:
int? a = 2;
int? b = 4;
int c = a ?? 0 + b ?? 0;
// Result:
// c = 2;
The obvious answer was a problem with operator precedence and a few brackets later fixed the problem:
int c = (a ?? 0) + (b ?? 0);
// Result:
// c = 6;
But why was it doing in the first instance? A little playing with linqpad later and it turns out the + operator has a much higher precedence than ??, so it was actually doing:
int c = a ?? ((0 + b) ?? 0);
This reads as: a, or if a is null then 0 + b, if 0 + b is null then zero.
The mistake I made was because I'm so used to using ?? as a simple substitution of the preceding variable I wasn't thinking of it as a 'real' operator with precedence and ordering.
