Curly Braces In C#

Question

I was playing around with some code and I was wondering if any can tell me what the curly braces in this code represents. I thought it would've been for an empty object but that doesn't seem to be the case.

 Person person = new Person{};

            if (person is {}){
                Console.WriteLine("Person is empty.");
            } else {
                Console.WriteLine("Person is not empty.");
            }

It compiles just fine; but if I populate the properties of the person class it still falls into the person is empty part of the if statement.

https://softwareengineering.stackexchange.com/questions/171710/creating-object-parameters-in — R10t--, Feb 06 '20 at 21:31
You have three different uses of curly braces in play here (block, object initializer, pattern matching), and links to explanations of two of them. For a usable answer, please indicate which one you're asking about. — madreflection, Feb 06 '20 at 21:32
I guess you answered my question. I'm referring to the if statement where person is {} ; so I'm assuming this if for pattern matching. — Tee, Feb 06 '20 at 21:38
It's an anonymous object that behaves like an empty `IEnumerable — Victor Wilson, Feb 06 '20 at 21:43
You are using [property patterns](https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#property-patterns) but with no requirement for a specific property value. — NetMage, Feb 06 '20 at 22:45

Robert J · Accepted Answer · 2020-08-20T10:27:46.717

10

{} means in this context a pattern matching of any type to check if the instance is not null:

if(person != null){     //the same as: if(person is {})...

}

It is like a var keyword for pattern matching, so you do not need to specify/repeat the type explicitly (although you know it).

if(GetPersonFromDb() is {} person){     //the same as: var person = GetPersonFromDb(); if(person != null)...

}

More info (see the section Special match expressions): https://hackernoon.com/whats-pattern-matching-in-c-80-6l7h3ygm

edited Aug 20 '20 at 10:27

answered Aug 20 '20 at 10:19

Robert J

704
10
8

4

Thanks. Still think `GetPersonFromDb() is var person` would have been much clearer to majority of C# devs, and we wouldn't be searching for "what it means". :) I miss the old C# team who were very very hard to sell on introducing "new" stuff like this. – vulcan raven Nov 16 '20 at 20:48

Curly Braces In C#

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