CA2231: Overload operator equals on overriding ValueType.Equals
TypeName | OverloadOperatorEqualsOnOverridingValueTypeEquals |
CheckId | CA2231 |
Category | Microsoft.Usage |
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) Else Return left.Equals(right) End If
if (Object.ReferenceEquals(left, null)) return Object.ReferenceEquals(right, null); return left.Equals(right);
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)); } } }
