Ternary operator associativity in C# - can I rely on it?

Question

Ahh, don't you just love a good ternary abuse? :) Consider the following expression:

true ? true : true ? false : false

For those of you who are now utterly perplexed, I can tell you that this evaluates to true. In other words, it's equivalent to this:

true ? true : (true ? false : false)

But is this reliable? Can I be certain that under some circumstances it won't come to this:

(true ? true : true) ? false : false

Some might say - well, just add parenthesis then or don't use it altogether - after all, it's a well known fact that ternary operators are evil!

Sure they are, but there are some circumstances when they actually make sense. For the curious ones - I'm wring code that compares two objects by a series of properties. It would be pretty nice if I cold write it like this:

obj1.Prop1 != obj2.Prop1 ? obj1.Prop1.CompareTo(obj2.Prop1) :
obj1.Prop2 != obj2.Prop2 ? obj1.Prop2.CompareTo(obj2.Prop2) :
obj1.Prop3 != obj2.Prop3 ? obj1.Prop3.CompareTo(obj2.Prop3) :
obj1.Prop4.CompareTo(obj2.Prop4)

Clear and concise. But it does depend on the ternary operator associativity working like in the first case. Parenthesis would just make spaghetti out of it.

So - is this specified anywhere? I couldn't find it.

Answer 1

Yes, you can rely on this (not only in C# but in all (that I know) other languages (except PHP … go figure) with a conditional operator) and your use-case is actually a pretty common practice although some people abhor it.

The relevant section in ECMA-334 (the C# standard) is 14.13 §3:

The conditional operator is right-associative, meaning that operations are grouped from right to left. [Example: An expression of the form a ? b : c ? d : e is evaluated as a ? b : (c ? d : e). end example]