C# { } operator

Question

I cannot find it anywhere. Could you tell me what the expression { } means in c# or give me a link to documentation.

Here is example usage which I have found in my project:

Method(IProfileDocument profileDocument)
{
    if(profileDocument.documentId is not { } documentId
    || string.IsNullOrEmpty(documentId))
    { 
       do something...
    }
}

Maybe this will help: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/basic-concepts#77-scopes — Ibrennan208, Sep 13 '22 at 05:57
The curly braces are a way to indicate scope, and show what is encapsulated within another member. — Ibrennan208, Sep 13 '22 at 05:58
You may also see them used in [String Interpolation](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/tokens/interpolated) — Ibrennan208, Sep 13 '22 at 06:00
You might also see them in an array or list declaration: `new int[] { 1, 2, 3 };` — Ibrennan208, Sep 13 '22 at 06:01
Otherwise you may be asking a duplicate of this question: https://stackoverflow.com/questions/62139886/meaning-of-curly-braces-after-the-is-operator — Ibrennan208, Sep 13 '22 at 06:02
Does this answer your question? [Meaning of curly braces after the "is" operator](https://stackoverflow.com/questions/62139886/meaning-of-curly-braces-after-the-is-operator) — mkrieger1, Sep 13 '22 at 08:39

score 5 · Accepted Answer · answered Sep 13 '22 at 06:02

5

{ } when used with is is an empty property pattern.

{ } is basically equivalent to != null

Read https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/patterns#property-pattern

answered Sep 13 '22 at 06:02

Piglet

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[This reference](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/patterns#property-pattern) has the exact `(s is {} x)` pattern seen in the question, and its equivalent statements. Admittedly, it is one of the weirdest constructs in the language.. – NPras Sep 13 '22 at 06:09
So what is the difference between (s is {} x) and (s is not {} x)? – Ellbar Sep 13 '22 at 06:18
not negates the pattern. the difference between `is` and `is not` should be self-explainatory :-) – Piglet Sep 13 '22 at 09:12

score 1 · Answer 2 · answered Sep 13 '22 at 06:33

Property Pattern: A property pattern checks that the input value is not null and recursively matches values extracted by the use of accessible properties or fields.

                string s =null;
                if (s is not { } documentId)
                {

                }
                else
                {
                    string mj = documentId;
                }

Declaration Pattern: The declaration_pattern both tests that an expression is of a given type and casts it to that type if the test succeeds. This may introduce a local variable of the given type named by the given identifier, if the designation is a single_variable_designation.

Here first check profileDocument.documentId is null or not. after that if not null then value asign to new a variable documentId.

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/patterns#property-pattern

C# { } operator

2 Answers2