encounter a crash with generic function in unity5.3/5.4 - unity3d

Question

I want simulate a functional programming Option class with map and flatMap but It can't work in Unity engine. as a example, I create three .cs file as follow:
1 .NET 2.0 default delegate is't covariance and contravariance, so I override it.
using System;
namespace Functional
{
public delegate R Func<out R>();
public delegate R Func<in A, out R>(A a);
public delegate R Func<in A, in B, out R>(A a, B b);
public delegate R Func<in A, in B, in C, out R>(A a, B b, C c);
public delegate R Func<in A, in B, in C, in D, out R>(A a, B b, C c, D d);
public delegate R Func<in A, in B, in C, in D, in E, out R>(A a, B b, C c, D d, E e);
public delegate void Action<in A>(A a);
}
2 define Option classes
using UnityEngine;
using System.Collections;
using Functional;
namespace Lorance.RxScoket.Util {
public interface IOption<out T> {
void Foreach (Action<T> func);
IOption<R> Map<R> (Func<T, R> func);
IOption<R> FlatMap<R> (Func<T, IOption<R>> func);
bool IsEmpty();
T Get ();
}
public static class IOptionEx {
public static T GetOrElse<T> (this IOption<T> opt, Func<T> defaultValue) {
return opt.IsEmpty() ? defaultValue() : opt.Get();
}
}
public abstract class Option<T>: IOption<T> {
public abstract bool IsEmpty ();
public abstract T Get ();
public void Foreach (Action<T> act) {
if (!IsEmpty ()) {
act (Get());
}
}
public IOption<R> Map<R>(Func<T, R> func) {
if (IsEmpty ())
return new None<R> ();
else
return new Some<R>(func (Get()));
}
public IOption<R> FlatMap<R>(Func<T, IOption<R>> func) {
if (IsEmpty ())
return new None<R> ();
else
return func (Get());
}
public static Option<T> apply(T value){
if (value == null)
return new None<T> ();
else
return new Some<T> (value);
}
public static Option<T> Empty = new None<T>();
}
public class Some<T> : Option<T> {
T value;
public Some(T value){
this.value = value;
}
public override bool IsEmpty() {return false;}
public override T Get() {
return value;
}
}
public class None<T> : Option<T> {
public override bool IsEmpty() {return true;}
public override T Get() {
throw new NoSuchElementException ("None.Get()");
}
}
public class NoSuchElementException : System.SystemException {
public NoSuchElementException(string message)
: base(message)
{
}
}
}
3 crash example
using UnityEngine;
using System.Collections;
using Lorance.RxScoket.Util;
public class TestFlatMap : MonoBehaviour {
// Use this for initialization
void Start () {
Dog d = new Dog ();
IOption<Dog> dogOpt = new Some<Dog> (d);
//ok
Dog dog = dogOpt.GetOrElse<Dog> (() => new Dog());
//crash at this point. does it care about polymorphism? but it works on pure .net project
Animal animal = dogOpt.GetOrElse<Animal> (() => new Cat());
print ("r2 -" + animal);
}
}
public class Animal {}
public class Dog: Animal {}
public class Cat: Animal {}
Does someone also meets the problem and how to solve it?
a complete crash example at : https://github.com/Unlimited-Works/crash-eg
Get the crash with this step:
1. Open the project with unity editor.
2. Open scene 'eg.unity'.
3. Press play.
4. result: Unity crashes.
it crashes when executing 'TestFlapMap.cs':
Animal animal = dogOpt.GetOrElse (() => new Cat());
if you also encounter the promblem please give me a vote at unity issues, it has delay one month ago and not any response from Unity official.
thanks