Default parameters should not be used

TypeName	DefaultParametersShouldNotBeUsed
CheckId	CA1026
Category	Microsoft.Design
Breaking Change	Breaking

Cause

An externally visible type contains an externally visible method that uses a default parameter.

Rule Description

Methods that use default parameters are allowed under the Common Language Specification (CLS); however, the CLS allows compilers to ignore the values assigned to these parameters. Code written for compilers that ignore default parameter values must explicitly provide arguments for each default parameter. To maintain the behavior that you want across programming languages, methods that use default parameters should be replaced with method overloads that provide the default parameters.

The C# compiler ignores the values of default parameters as does the Managed C++ compiler when accessing managed code. The Visual Basic compiler supports methods with default parameters using the Optional (Visual Basic) keyword.

How to Fix Violations

To fix a violation of this rule, replace the method that uses default parameters with method overloads that supply the default parameters.

When to Exclude Warnings

Do not exclude a warning from this rule.

Example

The following example shows a method that uses default parameters, and the overloaded methods that provide an equivalent functionality.

Imports System

<Assembly: CLSCompliant(True)>
Namespace DesignLibrary

    Public Class DefaultVersusOverloaded

        Sub DefaultParameters(Optional parameter1 As Integer = 1, _
                              Optional parameter2 As Integer = 5)
            ' ...
            Console.WriteLine("{0} : {1}", parameter1, parameter2)
        End Sub

        Sub OverloadedMethod()
            OverloadedMethod(1, 5)
        End Sub

        Sub OverloadedMethod(parameter1 As Integer)
            OverloadedMethod(parameter1, 5)
        End Sub

        Sub OverloadedMethod(parameter1 As Integer, parameter2 As Integer)
            ' ...
            Console.WriteLine("{0} : {1}", parameter1, parameter2)
        End Sub

    End Class

End Namespace

Related Rules

Replace repetitive arguments with params array

See Also

Concepts

Common Language Specification