CODEWITHSUNDEEP
c#operatorsoperator-overloading
user2128702
user2128702

Reputation: 2121

How to override the == operator

How can I define the operator == for instances of my class? I tried like this:

public bool operator == (Vector anotherVector)
{
    return this.CompareTo(anotherVector) == 1 ;              
}

but it says:

overloadable unary operator expected

Upvotes: 5

Views: 2049

Answers (3)

Habib
Habib

Reputation: 223257

You need to mark the method as static and also you have to implement not equal !=. 

public static bool operator ==(Vector currentVector,Vector anotherVector)
{
    return currentVector.CompareTo(anotherVector) == 1 ;              
}

You have to implement == for two objects.

AND for !=

AND 

public static bool operator !=(Vector currentVector,Vector anotherVector)
{
    return !(currentVector.CompareTo(anotherVector) == 1) ;
}

See: Guidelines for Overloading Equals() and Operator == (C# Programming Guide)

Overloaded operator == implementations should not throw exceptions. Any type that overloads operator == should also overload operator !=.

Upvotes: 9

r.net
r.net

Reputation: 631

I agree fully with Habib's answer - also +1 it... just don't forget to handle nulls.

public static bool operator ==(Vector left, Vector right)
        {
            if ((object)left == null)
                return (object)left == null;

            if ((object)right == null)
                return false;

            return ...;
        }

too big to post as his comment. Hope this helps.

Upvotes: 2

Ben Voigt
Ben Voigt

Reputation: 283644

Unlike C++, which allows operators to be defined as instance member functions so that the left operand becomes the this pointer, C# operator overloading is always done as static member functions.

There can be no this pointer, and both operands are explicit parameters.

public static bool operator==(Vector left, Vector right)
{
    return left.CompareTo(right) == 1;              
}

(Although this seems semantically incorrect, normally CompareTo returns zero for equivalence)

Upvotes: 4

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