Attribute on struct default constructor

Question

As structs cannot have explicit user-defined parameterless constructors e.g.

public struct MyStruct
{
    public MyStruct() { … } // Not allowed!
}

I was wondering if and how I can apply an attribute to that exact constructor. In the end, what I want to do is this (best would be if the parameterless constructor could be private, but that's not allowed either):

public struct MyStruct
{
    [Obsolete("Do not call the constructor directly, use MyStruct.Get() instead.")]
    public MyStruct() { … }

    public static MyStruct Get
    {
      // Important initializing here.
    }
}

Is there something like this fictional attribute target [constructor: Obsolete()] which allows for an attribute to be applied to the default constructor?

EDIT: Some more information.

The situation is this: I need to use MyStruct for P/Invoke and cannot use a class. I want to warn the user that they shouldn't get an instance of MyStruct because it misses important initialization, and they should rather use a factory method instead.

If you want that level of control, then you're probably going to have to use a class instead of a struct. — DavidG
– DavidG, Commented May 24, 2018 at 10:50
@DavidG you're right, it would be dead-simple if it could be a class. However, since it will be used for P/Invoke it needs to be a struct. — Thomas Flinkow
– Thomas Flinkow, Commented May 24, 2018 at 10:51
It's kind of XY problem, it would be great if you add some more details about your question and why you want to do such thing. — SᴇM
– SᴇM, Commented May 24, 2018 at 10:59
It won't really solve all problems, because struct can be initialized to default state without calling that constructor. And if that state is unacceptable to you - you have to verify manually then (obsolete constructor will not catch all problem cases). — Evk
– Evk, Commented May 24, 2018 at 11:02
You can use a class for P/Invoke - what makes you think you can't? It gets marshalled by the marshaller either way. Unless it's a struct embedded in another struct. — Matthew Watson
– Matthew Watson, Commented May 24, 2018 at 11:08

Hossein Golshani · Accepted Answer · 2018-05-24 11:28:15Z

1

Because of struct is a ValueType, by its nature you can't find any way.

even you instantiated a struct or not, it will be instantiated.

int x = new int(); is equivalent to int x;

and

MyStruct s = new MyStruct(); is equivalent to MyStruct s;

Suppose you can find a way to warn about MyStruct s = new MyStruct();. any definition to MyStruct s; is also warned! Then there is no way.

answered May 24, 2018 at 11:28

Hossein Golshani

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