Metadata

ID: csharp-best-practices/optional-ref-out

Language: C#

Severity: Info

Category: Best Practices

Description

The modifier Optional should not be used on ref or out parameters because it’s semantically incorrect:

• an out parameter is used as a value to return from the function and, therefore, is not optional
• a ref parameter is passed back to the caller

Non-Compliant Code Examples

class MyClass {

    public static void routine([Optional] out i)
    {
    }
}

class MyClass {
    public static void routine([Optional] ref int i)
    {
    }

}

Compliant Code Examples

class MyClass {
    // Safe: not using Optional with ref or out parameters
    public static void routine(ref int i)
    {
    }

    public static void anotherRoutine([Optional] int i)
    {
    }
}