Check if a type is managed inside a program

Question

I tried to write a code to check if a type is managed:

using System;
struct A
{
    public int a;
    public string s;
}
struct B<T> where T : unmanaged
{ }
class Program
{
    public static bool IsManaged<T>()
    {
        try
        {
            typeof(B<>).MakeGenericType(typeof(T));
        }
        catch (Exception)
        {
            return true;
        }
        return false;
    }
    static void Main()
    {
        if (IsManaged<A>())
            Console.WriteLine("Managed");
        else
            Console.WriteLine("Unmanaged");
    }
}

But the output is Unmanaged while A is not unmanaged by definition:

An unmanaged-type is any type that isn’t a reference-type or constructed type, and doesn’t contain reference-type or constructed type fields at any level of nesting.

Is the a way to fix the code or is there any other way to check if a type is managed?

isnt a `string` a reference type and since `A` has a nested `string` it would be `unmanaged` with regards to the definition you provided? — JohnChris, Jun 07 '19 at 10:17
I´m pretty sure `MakeGenericType` throws an exception, as `A` isn´t unmanaged and thus does not fit the generic constraint. — MakePeaceGreatAgain, Jun 07 '19 at 10:21
@JohnChris using `B` is illegal and it clearly proves that `A` isn't unmanaged regardless of definition. There is something wrong with `IsManaged` function above. — Minimus Heximus, Jun 07 '19 at 10:21
@HimBromBeere I run the code in VS 2019 and no exceptions is shown. — Minimus Heximus, Jun 07 '19 at 10:23
I assume that reflection isn't honouring the `unmanaged` constraint then. Perhaps a bug. — DavidG, Jun 07 '19 at 10:31
Hmya, there was a good reason why the original C# team did not want to implement this constraint, even though it has been available for 14 years. Beyond its horrible name, the runtime just doesn't have any problems creating the type. Even when you append `.MakePointerType()`, what the constraint really means. The runtime supports more than the language, can even come to a good end as long as the GC sees the pointer variable, it has to be the compiler that enforces the constraint. You can't do it. — Hans Passant, Jun 07 '19 at 10:46

Check if a type is managed inside a program

0 Answers0