AvoidDefaultValueSwitchParameter

Severity Level: Warning

Default state: Always enabled

Description

This rule detects switch parameters that are assigned a default value of $true. Switch parameters shouldn't have default values. By design, a switch parameter is $false when not specified and $true when included in the command. Assigning a default value of $true to a switch parameter violates this design principle and can cause unexpected behavior.

If your parameter needs to accept only true and false values, use the [Switch] type instead of [Boolean]. PowerShell automatically handles switch parameters correctly without requiring a default value.

To fix this issue, remove the default value from the switch parameter declaration. The switch naturally defaults to $false when not specified, allowing your logic to respond appropriately to the caller's input.

To learn more, see Strongly Encouraged Development Guidelines.

Example

Noncompliant

function Test-Script
{
    [CmdletBinding()]
    Param
    (
        [String]
        $Param1,

        [switch]
        $Switch=$True
    )
    ...
}

Compliant

function Test-Script
{
    [CmdletBinding()]
    Param
    (
        [String]
        $Param1,

        [switch]
        $Switch
    )

    ...
}

Configure rule

This rule is always enabled and isn't configurable. Use one of the following methods to avoid using this rule:

• Create a custom rule configuration file to include only the rules you want or exclude the rules you don't want.
• Add the appropriate rule suppression attributes to your code to suppress the rule for specific code blocks. For more information, see the Suppressing rules section of Using PSScriptAnalyzer.