等于返回意外结果

Question

Please see the code below:

public class ValueType<T> where T : class,new()
    {
        public virtual bool Equals(T other)
        {
            if (other == null)
                return false;
            Type t = GetType();
            Type otherType = other.GetType();
            if (t != otherType)
                return false;
            FieldInfo[] fields = t.GetFields(System.Reflection.BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
            foreach (FieldInfo field in fields)
            {
                object value1 = field.GetValue(other);
                object value2 = field.GetValue(this);
                if (value1 == null)
                {
                    if (value2 != null)
                        return false;
                }
                else if (!value1.Equals(value2))
                    return false;
            }
            return true;
        }
    }

    class Tiger : ValueType<Tiger> { public string name; public Tiger mother; }

    class Program
    {
        static void Main(string[] args)
        {
            Tiger t1 = new Tiger() { name = "Teri" }; 
            Tiger t2 = new Tiger() { name = "Teri" }; 
            Tiger t3 = new Tiger() { name = "Toni", mother=t1 };
            Tiger t4 = new Tiger() { name = "Toni", mother = t2 };
            bool Test1 = t4.mother.Equals(t3.mother); //Highlighed line
            bool Test2 = t4.Equals(t3);
        }
    }

I don't understand why the highlighted line returns false. I would expect it to run in an infinate loop.

Answer 1

Why you expect an infinite loop? Following returns true not false :

bool Test1 = t4.mother.Equals(t3.mother); . 

Isn't that expected because both mothers are equal? They have the same name and there's no "grandmom". Their mother field returns null since the Tiger is a reference type(class).

Why t4.Equals(t3) returns false ?

Because you have declared it as Object , so Object.Equals is used which just compares references. If you would try-cast it to Tiger this Equals would be called.

That's why this doesn't cause an infinite loop but just returns false (not the same reference):

...else if (!value1.Equals(value2))

Note that you haven't overridden Equals . You would get your expected behaviour if you'd do it:

class Tiger : ValueType<Tiger> {
    public string name; public Tiger mother;
    public override bool Equals(object obj)
    {
        return ((ValueType<Tiger>) obj).Equals(this);
    }
}

Now this works as expected. It won't cause an infinite recursion because at some time the parent mother will be null , but it will check recursively if also the mothers are equal.

Another way would be to change the signature of the already existing Equals in ValueType :

public override bool Equals(Object other)