IsTrue:TrueCondition:FalseCondition Evaluates Both Conditions

Question

I discovered a very puzzling behavior for the following code:

public double ReturnBehavior(List<double> ptList)
{
    return ptList.Count==0? 0:ptList[0];
}

I thought it should be equivalent to

public double ReturnBehavior(List<double> ptList)
{
    if(ptList.Count==0)
       return 0;
    return ptList[0];
}

But it is not, because the first method will evaluate both true and false condition together. So this means that first method will try an IndexOutOfRange exception if ptList.Count==0.

Am I missing something here? Or is it a bug in vs 2008?

Answer 1

They ought to behave the same. The ternary operator uses short-circuit semantics. If the test passes, only the first expression is evaluated, otherwise, only the second expression is evaluated. Are you actually seeing an exception?

Answer 2

No IndexOutOfRange exception in VS2010.

Answer 3

I've checked both in VS2010 and VS2008, behavior is expected - no exceptions. If you have errors - they are not in the given code fragment

Answer 4

I think that in some cases, if you have a multicore processor, the compiler will tell the processor to evaluate ahead if possible. At least i know that's the case when for example i have an if(condition1 && condition2), on some computers it will evaluate both conditions in parallel, and this means it evaluates the second condition even if the first fails.