CA2225: Operator overloads have named alternates

Item Value
RuleId CA2225
Category Microsoft.Usage
Breaking change Non-breaking

Cause

An operator overload was detected and the expected named alternative method was not found.

By default, this rule only looks at externally visible types, but this is configurable.

Rule description

Operator overloading allows the use of symbols to represent computations for a type. For example, a type that overloads the plus symbol + for addition would typically have an alternative member named Add. The named alternative member provides access to the same functionality as the operator. It's provided for developers who program in languages that do not support overloaded operators.

This rule examines:

  • Implicit and explicit cast operators in a type by checking for methods named To<typename> and From<typename>.

  • The operators listed in the following table:

C# Visual Basic C++ Alternate method name
+ (binary) + + (binary) Add
+= += += Add
& And & BitwiseAnd
&= And= &= BitwiseAnd
| Or | BitwiseOr
|= Or= |= BitwiseOr
-- N/A -- Decrement
/ / / Divide
/= /= /= Divide
== = == Equals
^ Xor ^ Xor
^= Xor= ^= Xor
> > > CompareTo or Compare
>= >= >= CompareTo or Compare
++ N/A ++ Increment
!= <> != Equals
<< << << LeftShift
<<= <<= <<= LeftShift
< < < CompareTo or Compare
<= <= <= CompareTo or Compare
&& N/A && LogicalAnd
|| N/A || LogicalOr
! N/A ! LogicalNot
% Mod % Mod or Remainder
%= N/A %= Mod
* (binary) * * Multiply
*= N/A *= Multiply
~ Not ~ OnesComplement
>> >> >> RightShift
= N/A >>= RightShift
- (binary) - (binary) - (binary) Subtract
-= N/A -= Subtract
true IsTrue N/A IsTrue (Property)
- (unary) N/A - Negate
+ (unary) N/A + Plus
false IsFalse False IsTrue (Property)

*N/A means the operator cannot be overloaded in the selected language.

Note

In C#, when a binary operator is overloaded, the corresponding assignment operator, if any, is also implicitly overloaded.

How to fix violations

To fix a violation of this rule, implement the alternative method for the operator. Name it using the recommended alternative name.

When to suppress warnings

Do not suppress a warning from this rule if you're implementing a shared library. Applications can ignore a warning from this rule.

Configurability

You can configure which parts of your codebase to run this rule on, based on their accessibility. For example, to specify that the rule should run only against the non-public API surface, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.ca2225.api_surface = private, internal

You can configure this option for just this rule, for all rules, or for all rules in this category (Usage). For more information, see Configure .NET code-quality analyzers.

Example

The following example defines a structure that violates this rule. To correct the example, add a public Add(int x, int y) method to the structure.

using System;

namespace UsageLibrary
{
    public struct Point
    {
        private int x,y;
        
        public Point(int x, int y)
        {
            this.x = x;
            this.y = y;
        }

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

        // Violates rule: OperatorOverloadsHaveNamedAlternates.
        public static Point operator+(Point a, Point b)
        { 
            return new Point(a.x + b.x, a.y + b.y);
        }

        public int X {get {return x;}}
        public int Y {get {return x;}}
    }
}