检查开关参数的正确方法是什么

检查开关值的正确方法是什么？

function testSwitch
{
    Param(
        [switch] $swth
    )

    Write-Host "Value of swth is $swth"

    if($swth.IsPresent){
        Write-host "Switch is present"
    }
    if($swth){
        Write-Host "Switch is present"
    }

}

testSwitch -swth

我知道两个 if 语句都可以正常工作，但是如何呢？

$swth.IsPresent and $swth can be used interchangeably, because in a Boolean context (such as an if conditional) $swth (an instance of type [switch] https://learn.microsoft.com/en-us/dotnet/api/system.management.automation.switchparameter representing a switch parameter https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_functions_advanced_parameters?view=powershell-6#switch-parameters) effectively returns the value of the .IsPresent property.^[1]

In fact, $swth is probably preferable^[2], not just for concision, but because the .IsPresent property is somewhat confusingly named:

.IsPresent并不表示presence开关本身，但它是否值为$true.

单独指定开关时 --swth- 暗示both，如果您明确将其设置为，则情况并非如此$false：通过-swth:$false makes .IsPresent return $false，即使开关很明显present.

Passing $false明确地并不常见，但有其用途，例如选择退出确认提示时-Confirm:$false， 什么时候以编程方式构建论据。

所以，如果你想区分用户没有通过交换机和用户传递它的值$false, .IsPresent不会帮助你 - 你必须使用$PSBoundParameters.ContainsKey('swth')

^{[1] On conversion to Boolean, which happens in method LanguagePrimitives.IsTrue() https://github.com/PowerShell/PowerShell/blob/bbd54c317e01d652081753a9cd2350e96aa8bd3e/src/System.Management.Automation/engine/LanguagePrimitives.cs#L1013, PowerShell calls a [switch] instance's .ToBool() method https://github.com/PowerShell/PowerShell/blob/bbd54c317e01d652081753a9cd2350e96aa8bd3e/src/System.Management.Automation/engine/MshCmdlet.cs#L108, which in turn returns the private backing variable behind the .IsPresent property.}

^{[2] The only caveat is that you must be aware that $swth is not a Boolean ([bool]), but of type [switch], which may matter in other contexts.}