Plugged System.Activator.CreateInstance methods for types with parameterless constructors.

[Guillermo-Santos]

This PR add the plugs for System.Activator.CreateInstance<T>() and System.Activator.CreateInstance(Type T, bool, bool) two methods that are used to create generic types.

With System.Activator.CreateInstance<T>() the following start to work on cosmos:

// A generic method to get an instance of type T
public static T Get<T>() where T : class, new()
{
    return new T();
}

Limitations

1. Constructors may not be on the compilation result:At the moment Constructors, as any other method, are not included on the compilation result if never called, this could cause stack corruption or null reference exceptions when calling one of these methods or when using its result.

To avoid this, you would need to add a dummy variable somewhere (BeforeRun recommended) to make IL2CPU include the ctor on the compilation.

var dummy = new MyClass();
var myVar = Activator.CreateInstance<MyClass>();//This will work as ctor is included on the compilation.

2. ref struct should not be supported: If the type you are trying to instantiate is a ref struct these methods should throw a NotSupportedException (as far as I know, is because ref struct should never be boxed), but since, at the moment, we cannot check if a type is a ref struct (System.Type.IsByRefLike field not plugged) we just process the ref struct and return it as a normal struct or class.

[zarlo]

ref struct should not be supported: If the type you are trying to instantiate is a ref struct these methods should throw a NotSupportedException (as far as I know, is because ref struct should never be boxed), but since, at the moment, we cannot check if a type is a ref struct (System.Type.IsByRefLike field not plugged) we just process the ref struct and return it as a normal struct or class.

@Guillermo-Santos if it has not already been done could you make a issue for this so we can track it

[zarlo]

is there a way to prevent the Stack Corruption and just throw an exception (we should try and match what .net does whti what exception is thrown)

[Guillermo-Santos]

The problem is, we do not have method info, we do not know what method is a ctor and what method is not (and their parameters) at runtime. To make it all work as intended the Vtable should be reworked.

[Guillermo-Santos]

What i mean for stack corruption or null reference, is that a method other than the ctor was called or for some reason the null check of the ctor throws (happened while testing but should not happend now). This could happend either because there is no parameterless constructor or that ctor is not the address at index 0 (till now, it always have been at index 0, but the possibility of it changing is still there).

[Guillermo-Santos]

ref struct should not be supported: If the type you are trying to instantiate is a ref struct these methods should throw a NotSupportedException (as far as I know, is because ref struct should never be boxed), but since, at the moment, we cannot check if a type is a ref struct (System.Type.IsByRefLike field not plugged) we just process the ref struct and return it as a normal struct or class.

@Guillermo-Santos if it has not already been done could you make a issue for this so we can track it

Will do

[quajak]

Great work!