C# .NET how null is casting in anonymous type?

Question

This code will not compile:

        var x = new {
            Property = null,
        };

With following exception: Cannot assign null to anonymous type property

But this will work fine:

        var someBool = false;
        var x = new {
            Property = someBool ? "value" : null,
        };

I think there is implicit casting something like this - (string)null but not exactly sure.

So I would like to know more about this case and how this works internally (I didn't find any article explaining this)

So read the answer carefully: "so that the compiler knows which type you want for that property". — Roman Ryzhiy
– Roman Ryzhiy, Commented Dec 8, 2022 at 19:23

Guru Stron · Accepted Answer · 2022-12-08 19:37:52Z

5

Compiler needs to determine type for anonymous type's properties which can't be done from just null (though you can argue about using object in this case but see the following quote), on the contrary ternary operator has a type (see the linked docs explaining how compiler determines it), which is string in case of someBool ? "value" : null.

From anonymous types doc:

The expression that is used to initialize a property cannot be null, an anonymous function, or a pointer type.

edited Dec 8, 2022 at 19:37

answered Dec 8, 2022 at 19:22

Guru Stron

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1 Comment

Roman Ryzhiy Over a year ago

string? actually.

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