C# Null Conditional Operator inside method argument

Question

I have following methods:

float myMethod(MyObject[][] myList) 
{
      float a = 0;
      if (myListProcessingMethod(myList?.Where(x => x.mySatisfiedCondition()).ToList()))
      {
            a = 5;
      }
      return a;
}

bool myListProcessingMethod(List<MyObject[]> myList)
{
      bool isSuccess = false;
      if (myList.Any())
      {
            isSuccess = true;
      }
      return isSuccess;
}

I consider this condition:

if (myListProcessingMethod(myList?.Where(x => x.mySatisfiedCondition()).ToList()))

I refactor my condition to:

if (myList?.Length != 0)
{
      if (myListProcessingMethod(myList.Where(x => x.mySatisfiedCondition()).ToList()))
      {
            a = 5;
      }
}

Is this two conditions are equivalent? What is equivalent condition to first NullConditionOperator in traditional way? What is equivalent condition to second traditional checking using NullConditionalOperator?

List<T> doesn't have a Length property. Did you mean Count? Could you provide a minimal reproducible example and test the code for yourself first? Note that if myList is null, myList?.Count is null, which isn't equal to 0 - so you'd then end up with an exception. — Jon Skeet
– Jon Skeet, Commented Apr 12, 2018 at 10:54
myListProcessingMethod() can be boiled down to return myList.Any(); essentially. — Steve
– Steve, Commented Apr 12, 2018 at 10:59
I edit my question: Actually I have an 2 dimensional array of Object in first method arrgument — ElConrado
– ElConrado, Commented Apr 12, 2018 at 11:01
Why don't you just say if (myList?.Any(x => x.satisfiesCondition()) ?? false) { a = 5; }? — user9539019
– user9539019, Commented Apr 12, 2018 at 11:11

Andrei Tătar · Accepted Answer · 2018-04-12 11:05:09Z

3

The statement below can crash. If myList is null, myList?.Length will be null and myList?.Length != 0 will be true. That means myList.Where may crash with a null reference exception.

if (myList?.Length != 0)
{
  if (myListProcessingMethod(myList.Where(x => x.mySatisfiedCondition()).ToList()))
  {
        a = 5;
  }
}

you probably want

if (myList?.Length > 0) 
...

which will evaluate to true only if the list is not null and its Length is grater than 0.

answered Apr 12, 2018 at 11:05

Andrei Tătar

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3 Comments

Andrei Tătar Over a year ago

maybe he doesn't use the System.Collection.Generic.List. You're missing the point @Badiparmagi

ElConrado Over a year ago

@Andrew is it possible to join this two if statement as myListProcessingMethod argument?

Andrei Tătar Over a year ago

@ElConrado you can use && instead of 2 ifs... or what do you mean? You can also make myListProcessingMethod an extension method so you can chain it at the end, after ToList.

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