How to compare two elements of the same but unconstrained generic type for equality? [duplicate]

Question

Possible Duplicate:
Can’t operator == be applied to generic types in C#?

I've got the following generic class and the compiler complains that "Operator '!=' cannot be applied to operands of type 'TValue' and 'TValue'" (see CS0019):

public class Example<TValue>
{
    private TValue _value;
    public TValue Value
    {
        get { return _value; }
        set
        {
            if (_value != value) // <<-- ERROR
            {
                _value= value;
                OnPropertyChanged("Value");
            }
        }
    }
}

If I constrain TValue to class, I could use Object.Equals(). Since I need this for boths structs and classes I'd be very happy if I could avoid that though.

So the question is, how can I compare two elements of the same but unconstrained generic type for equality?

Answer 1

Did you try something like this?

public class Example<TValue>
{
    private TValue _value;
    public TValue Value
    {
        get { return _value; }
        set
        {

            if (!object.Equals(_value, value))
            {
                _value = value;
                OnPropertyChanged("Value");
            }
        }
    }
}

Answer 2

Three options:

• Constrain TValue to implement IEquatable<TValue> and then call x.Equals(y)
• Take another parameter of type IEqualityComparer<TValue> and use that
• Use EqualityComparer<TValue>.Default to perform the comparisons

You could always mix and match options 2 and 3, of course - default to the default comparer, but also allow a specific one to be provided.

Answer 3

• Equals() for value types
• ReferenceEquals() for reference types

Answer 4

Is IComparable an option?

public class Example<TValue> where TValue: IComparable
{
    private TValue _value;
    public TValue Value
    {
        get { return _value; }
        set
        {

            if (_value.CompareTo(value) != 0)
            {
                _value = value;
                OnPropertyChanged("Value");
            }
        }
    }
}

Answer 5

I think the != operator cannot be applied here because there are cases where it can't be used. For instance, != can't be used for comparing structs, unless the compare operators (== !=) are overloaded.

Of course, you can compare language structs, like int != int, but I'm not sure how this is implemented.

So, because TValue can be a custom struct, it cannot use the != operator.

Answer 6

public static bool operator ==(EntityBase<T> entity1, EntityBase<T> entity2)
        {
            if ((object)entity1 == null && (object)entity2 == null)
            {
                return true;
            }

            if ((object)entity1 == null || (object)entity2 == null)
            {
                return false;
            }

            if (Comparer<T>.Default.Compare(entity1.Id, entity2.Id) != 0)
            {
                return false;
            }

            return true;
        }