runtime: System.TypeLoadException thrown by the Runtime when using structs and generics

The following snippet of code, when compiled and run as a standalone program, will compile just fine but throw a runtime exception:

struct A
{
    B<A> b;

    static void Main(string[] args)
    {
        A a = new A();
    }
}

struct B<T>
{
    C<T> c;
}

class C<T>
{
    T t;
}

Exception thrown: Unhandled Exception: System.TypeLoadException: Could not load type 'A' from assembly 'dotnet, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

I have tested this with the newest public release of .NET Core I could find - 2.2.100-preview2-009404.

The same issue also occurs when building a standard .NET Framework project; I have tested targeting versions 4.5.2 and 4.7.2. Running the executable produced for .NET with mono (Mono JIT compiler version 5.14.0 (Visual Studio built mono)) works just fine - the program prints nothing and exits with code 0.

The same problem occurs if similar code is compiled into a DLL that’s later loaded as a library. However, this is the minimum repro case I could come up with. Should I separately file a bug for .NET Framework? This page suggests I should do so, but points to a “retired” web page.

About this issue

Original URL
State: closed
Created 6 years ago
Reactions: 4
Comments: 16 (10 by maintainers)

Most upvoted comments

@gafter

Why does nobody seem particularly interested in addressing this very fundamental bug - the current inability of the C# compiler to correctly process legal source code? I would have thought that these kinds of bugs would be given a high priority since this is quite legal source code.

Korporal on May 2, 2019

Your declaration is infinitely recursive. If every instance of struct A should contain B<A> which contains C<A> which contains A, then the struct would have to be infinitely big, that is obviously not possible (in this case it is otherwise empty, but empty structs in .net takes 1 byte anyways).

~~You could question whether Roslyn should detect this and fail with CS0523, but note that it can only do so if all the types are declared in the same assembly.~~

Sorry, I didn’t notice C being a class.

poizan42 on Oct 2, 2018

For the record, the repro from the top can be simplified to:

struct A
{
    B<A> b;

    static void Main(string[] args)
    {
        A a = new A();
    }
}

struct B<T>
{
    object c;
}

jkotas on Jun 5, 2019

@svick - That’s OK, it easy to misconstrue someone’s intentions here sometimes! NP.

Korporal on May 3, 2019