does c# null-conditional operator works with linq methods

Question

I am trying to use elvis operator to achieve something like this

List<string> list = new List<string> { "str1", "str2", "str3"};

string searchkey = "str4"; // this does not exist in the list so will use elvis operator before picking the first from the resulting sequence.

var result = list.where(s=>(s.Contains(searchkey)))?.First();

I expect result to be null but the code actually throws an exception.

1. That's not the Elvis Operator, 2. Where should be capitalized, 3. Where will never return null — D Stanley
– D Stanley, Commented Sep 8, 2016 at 20:00
Also, is your actual requirement "return the item if it's in the list, otherwise return the first item in the list"? — D Stanley
– D Stanley, Commented Sep 8, 2016 at 20:02
This is called the Null Conditional Operator, not the Elvis operator, as D Stanley mentioned: msdn.microsoft.com/en-us/library/dn986595.aspx — David L
– David L, Commented Sep 8, 2016 at 20:04

Sergey Kalinichenko · Accepted Answer · 2016-09-08 20:03:07Z

2

The problem is that

list.Where(s=>(s.Contains(searchkey)))

does not return null; it returns an empty sequence, which is not the same thing.

If you would like to get a null when the sequence of objects is empty, use FirstOrDefault:

var result = list.FirstOrDefault(s=>(s.Contains(searchkey)));

Note: C#'s version of "Elvis Operator" is ||, not ?.. The operator in your code is called null conditional operator.

answered Sep 8, 2016 at 20:03

Sergey Kalinichenko

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1 Comment

Bill Tür stands with Ukraine Over a year ago

'||' is logical or; '?.' is indeed the elvis operator

Halis S. · Accepted Answer · 2016-09-08 20:06:53Z

0

Because Where operator returns anything to enumerate and First() cannot be evaluated. You may use FirstOrDefault()

edited Sep 8, 2016 at 20:06

answered Sep 8, 2016 at 20:02

Halis S.

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2 Comments

D Stanley Over a year ago

"Where operator returns null" no it doesn't...

Halis S. Over a year ago

Ok it doesn't return null, but returns no element to iterate. I will edit. By the way, thank you for heads up.

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