# No Operator == on Reference Types
# Detects operator== overloading on reference types in C#
id: no-operator-eq-reference
name: operator== Should Not Be Overloaded on Reference Types
severity: warning
category: maintainability
defect_class: correctness
inline_tier: warning
language: csharp

message: "operator== should not be overloaded on reference types"

description: |
  Overloading == on reference types can cause confusion between
  reference equality and value equality. Let reference types use
  the default reference equality, or implement IEquatable<T>.

  ✅ FIX: Don't overload == for classes, use Equals() or make it a struct

  ```csharp
  public class Person : IEquatable<Person> {
      public bool Equals(Person other) {  // Explicit interface
          // Value equality logic
      }
  }
  ```

query: |
  (class_declaration
    body: (declaration_list
      (operator_declaration
        ("operator")
        ("==") @OP) @OPERATOR))

metavars:
  - OP
  - OPERATOR

tags:
  - maintainability
  - csharp
  - api-design
  - pitfall

examples:
  bad: |
    public class Person {
        public static bool operator ==(Person a, Person b) {  // BAD
            return a.Name == b.Name;
        }
    }

  good: |
    public struct Point {  // GOOD - value type
        public static bool operator ==(Point a, Point b) {
            return a.X == b.X && a.Y == b.Y;
        }
    }

has_fix: false