带有 var 的匿名类型给出错误 CS0825

Question

I want to create an anonymous type in C# inside a class.

The examples I have seen use var to create an anonymous variable

    var RecordId = new 
    { 
        Foo = 0,
        Bar = "can be also a string"
    };

However I want to create my anonymous variable inside a class.

public class Logger //: LogBase
{
    var RecordId = new 
    { 
        Foo = 0,
        Bar = 1
    };
}

So when Logging I can do:

Logger.RecordId.Foo

But declaring my anonymous type as var triggers the following error:

CS0825: The contextual keyword 'var' may only appear within a local variable declaration.

What is the type of an anonymous variable, so I don't have to use var?

I understand what the error is telling me, but I don't want to move my variable inside a function, it needs to be a property of Logger.

Edit: enum is what I tried t the beginning, but I need the values to be more flexible than just integers (like strings, so I can dump jon files). I updated my question to reflect that.

Answer 1

var (and by definition anonymous types) can only be declared inside a method, the error message is basically telling you that. If you need this type to be at class level, then make a class/struct/tuple to store it.

public static class Record
{
    public static int Foo { get; set; }
    public static int Bar { get; set; }
}

public class Logger //: LogBase
{
    public static Record RecordId { get; set; } = new Record();
}

Now you can do this:

var foo = Logger.RecordId.Foo;

Note that I also used static so you don't need to create a new instance of the class, but change that if you think it's relevant.

Answer 2

public class Logger //: LogBase
{
    public enum RecordId 
    { 
        Foo = 0,
        Bar = 1
    }
}

If you do not want strings you can do the above.

public class LogCategory
{
    private LogCategory(string value) { Value = value; }

    public string Value { get; private set; }

    public static LogCategory Foo { get { return new LogCategory("Foo"); } }
    public static LogCategory Bar { get { return new LogCategory("Bar"); } }

}

If you want strings you could create your own class something like the above.

Answer 3

You can use the dynamic type to have an anonymous instance variable.

public class Foo
{
    dynamic bar = new {
        A = 1,
        B = 2
    };
    
    public void Print() {
        Console.WriteLine(bar.A);   
    }
}

Try it out!

---

Just because you can do this doesn't mean it's a good idea. See DavidG 's answer for an alternative using a strongly-typed object that will not require you to expose your code to the many problems associated with the dynamic type .