CA2231: Overload operator equals on overriding ValueType.Equals
Collapse the table of content
Expand the table of content

CA2231: Overload operator equals on overriding ValueType.Equals








Breaking Change

Non Breaking

A value type overrides Object.Equals but does not implement the equality operator.

In most programming languages there is no default implementation of the equality operator (==) for value types. If your programming language supports operator overloads, you should consider implementing the equality operator. Its behavior should be identical to that of Equals.

You cannot use the default equality operator in an overloaded implementation of the equality operator. Doing so will cause a stack overflow. To implement the equality operator, use the Object.Equals method in your implementation. For example:

If (Object.ReferenceEquals(left, Nothing)) Then
    Return Object.ReferenceEquals(right, Nothing)
    Return left.Equals(right)
End If

if (Object.ReferenceEquals(left, null)) 
    return Object.ReferenceEquals(right, null);
return left.Equals(right);

To fix a violation of this rule, implement the equality operator.

It is safe to suppress a warning from this rule; however, we recommend that you provide the equality operator if possible.

The following example defines a type that violates this rule.

using System;

namespace UsageLibrary
    public struct PointWithoutHash
        private int x,y;

        public PointWithoutHash(int x, int y)
            this.x = x;
            this.y = y;

        public override string ToString()
            return String.Format("({0},{1})",x,y);

        public int X {get {return x;}}

        public int Y {get {return x;}}

        // Violates rule: OverrideGetHashCodeOnOverridingEquals.
        // Violates rule: OverrideOperatorEqualsOnOverridingValueTypeEquals.
        public override bool Equals (object obj)
            if (obj.GetType() != typeof(PointWithoutHash))
                return false;

            PointWithoutHash p = (PointWithoutHash)obj;   
            return ((this.x == p.x) && (this.y == p.y));


© 2015 Microsoft