LINQ All returns True if the size of the collection is 0.

[EvgenyMarchuk]

Description

I'm getting true for the zero size collection, using LINQ All to check that all items have a value

Reproduction Steps

var list = new List<string>();
var isTrue = list.All(x => x == "a");
Console.WriteLine(isTrue);

Expected behavior

False

Actual behavior

True

Regression?

No response

Known Workarounds

No response

Configuration

.net8.0.404
Win10, x64

Other information

If I'm not mistaken, the same is in .net9

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[stephentoub]

Thanks, but this is by design. Every item meets the criteria. There just aren't any items.

Per the docs:
"true if every element of the source sequence passes the test in the specified predicate, or if the sequence is empty; otherwise, false."

[maikschott]

@EvgenyMarchuk If you don’t want that behavior, you can use list.DefaultIfEmpty().All(x => x == "a"); which turns an empty enumeration to a non-empty enumeration filled with one element of value default(T).

[EvgenyMarchuk]

I was confused about this. It's very strange to 'say' true if item is empty.
I hadn't checked the documentation before the ticket was created.
Thanks for your help!

[ufcpp]

That question is probably better suited to StackOverflow.
https://stackoverflow.com/questions/7884888/why-does-enumerable-all-return-true-for-an-empty-sequence

[julealgon]

I was confused about this. It's very strange to 'say' true if item is empty. I hadn't checked the documentation before the ticket was created. Thanks for your help!

@EvgenyMarchuk this goes much further than C#: it is a logical "rule". Here is another question related to it from a Math perspective:

• https://math.stackexchange.com/questions/202452/why-is-predicate-all-as-in-allset-true-if-the-set-is-empty

It may sound strange at first, but it is the most correct way to implement this logical operator.