anonymous object initialisation with single variable

Question

I found have found such a line:

var myObject = new MyClass { 42 };

And I would like to know if it is possible to perform such operation. Documentation says that ,,You must use an object initializer if you're defining an anonymous type" so this is obvious but I cant find anything about alone integer in braces.

score 7 · Answer 1 · answered Jul 28 '16 at 10:43

7

No, but you can either call a constructor;

new MyClass(42)

if one is defined, or set any settable properties like this;

new MyClass { MeaningOfLife=42 };

answered Jul 28 '16 at 10:43

Steve Cooper

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This answer is wrong. The code presented in the question is perfectly valid for a collection initializer. – Enigmativity Jul 28 '16 at 11:10

score 3 · Accepted Answer · answered Jul 28 '16 at 11:07

The code you've provided isn't a class initializer or for anonymous types. The kind of class that this works for is a collection, but it can be defined minimally as this:

public class MyClass : IEnumerable<int>
{
    private List<int> _list = new List<int>();

    public void Add(int x)
    {
        Console.WriteLine(x);
        _list.Add(x);
    }

    public IEnumerator<int> GetEnumerator()
    {
        return _list.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return _list.GetEnumerator();
    }
}

Now you can run the code from your question:

var myObject = new MyClass { 42 };

You will get 42 written to the console.

The syntax is a collection initializer syntax and it basically requires the class to implement IEnumerable<T> and have a public Add(T value) method.

You can then add multiple values too:

var myObject = new MyClass { 42, 43, 44 };

anonymous object initialisation with single variable

2 Answers2