引用PowerShell类方法的参数？[Ref][Uint64]

Question

我有一个powershell类，我需要将它作为对UInt64变量的引用传递给它，并从该方法返回一个值。我正在尝试做一些类似下面的代码，但它给我一个语法错误。

也许我不需要加什么?裁判？因为所有变量在powershell中都是默认的引用，包括uint64？但我只是不确定这是不是真的...如果我遵循普通的C语言约定，那么该方法将获得参数的副本，而不是对变量的实际引用。我似乎在C#中回想起一些关于装箱和拆箱int类型的事情……boxing and unboxing c# int type如何使用boxing Int for Powershell类方法？

class PowerHe11 {

    # Constructor
    PowerHe11() {
    }

    [void]AccessChannel(
        [UInt64]$ichan,
        [UInt64]$idata,
        [UInt64]$isize,
        [UInt64]$ireal,    
        [ref][UInt64]$otimeout,
        [ref][UInt64]$odata,
        [ref][UInt64]$ochan,
        [ref][UInt64]$osize

    ) {                  
        $osize = 64;  #Return this value to caller of method
    }
}

错误消息为：

At C:\Users\wmoore\Documents\fpga\zynq_pl\run_ps1\Untitled1.ps1:13 char:11
+         [ref][UInt64]$otimeout,
+              ~~~~~~~~
Multiple type constraints are not allowed on a method parameter.
At C:\Users\wmoore\Documents\fpga\zynq_pl\run_ps1\Untitled1.ps1:14 char:14
+         [ref][UInt64]$odata,
+              ~~~~~~~~
Multiple type constraints are not allowed on a method parameter.
At C:\Users\wmoore\Documents\fpga\zynq_pl\run_ps1\Untitled1.ps1:15 char:14
+         [ref][UInt64]$ochan,
+              ~~~~~~~~
Multiple type constraints are not allowed on a method parameter.
At C:\Users\wmoore\Documents\fpga\zynq_pl\run_ps1\Untitled1.ps1:16 char:14
+         [ref][UInt64]$osize
+              ~~~~~~~~
Multiple type constraints are not allowed on a method parameter.
    + CategoryInfo          : ParserError: (:) [], ParentContainsErrorRecordException
    + FullyQualifiedErrorId : MultipleTypeConstraintsOnMethodParam

Answer 1

Your own answer展示了解决方案；让我添加一个解释和背景信息：

about_Ref是官方的帮助主题。

简而言之：

• [ref]**'s的主要用途是支持** ref out methods中的和 .NET 参数；例如，要调用System.Int32.TryParse方法，请使用以下命令：

- `[int] $int = 0; [int]::TryParse('42', [ref] $int)`

- Note that the **variable's type must match the type expected by the .NET method**, and that the only way to create a variable in PowerShell is to also assign it a value (even if that value is irrelevant, as is the case with the `out` parameter at hand); the `[ref]` cast is required (analogous to the need to use `ref` or `out` in C#.

- You may pass `[ref] $null` if you're not interested in the value being assigned by the method.

• While you can use it in PowerShell代码，这样做是笨拙的，如您的示例所示：

- **PowerShell code that receives a** **`[ref]`** **argument must refer to its value via the** **`.Value`** **property**, as your answer shows.

- **You** _**cannot type-constrain**_ **such a parameter**, so you lose type safety.

    - Note that in _function and scripts_ - as opposed to custom-class _methods_ - it is _syntactically allowed, but pointless_ to use both `[ref]` and a target data type (such as `[ref][UInt64]$otimeout` in your example), because the latter is effectively _ignored_; e.g.:

        - `function foo { param([ref] [int] $p) $p.Value += '!' }; $bar = 'none'; foo ([ref] $bar); $bar`

        - The call succeeds and `$bar` contains `'none!'`, which implies that the `[int]` type constraint was ignored.

- Calling scripts and functions requires [argument-mode syntax](https://stackoverflow.com/a/48779223/45375) (shell-like, whitespace-separated arguments, bareword strings allowed), making the `[ref]`-cast invocation more awkward by requiring `(...)` around the argument, as shown above (`foo ([ref] $bar)`).

- With respect to use in custom PowerShell `class`es, note that [**PowerShell's class support**](https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_Classes) **is - by design -** _**not**_ **on par with that of OO-focused languages such as** **`C#`**; that said, enhancements are planned; unfortunately, even the limited feature set still has problem as of PowerShell 7.1 - see [GitHub issue #6652](https://github.com/PowerShell/PowerShell/issues/6652).

有关 [ref]的技术背景

与C#中的ref不同，is a language keyword：it is a ，即[System.Management.Automation.PSReference] (其是[ref])。

因此，像[ref] $var这样的表达式是隐式构造[ref]实例的强制转换，绑定到[ref]-typed参数需要该实例。

警告

因为您不能直接使用通常等价的[ref]构造函数表达式作为强制转换[ref] $var的替代方法，所以

• 强制转换中包含了[ref]::new($var)解析器的魔力。
• PowerShell需要魔法才能知道$var引用的是一个变量对象本身，而不是像表达式中通常那样引用变量的值--后者确实是[ref]::new($var)的结果--$var的值被包装在一个[ref] [ref] $var的真正构造函数中，这个构造函数与[ref] $var是等价的

# BROKEN: Do not use a constructor - [ref]::new($int) - 
#         in lieu of a cast - [ref] $int
PS> [int] $int = 0; $null = [int]::TryParse('42', [ref]::new($int)); $int
0 # !! $int was NOT updated, because its *value* was wrapped in a [ref] instance

• It通常仅在使用带有[ref] operand.

的变量(对象)的转换时才有意义

- PowerShell lets you pass any value as the operand, which technically works, but makes no sense unless you explicitly save _the_ _`[ref]`_ _instance_ in a variable, pass _it_ as the argument, and then use the `[ref]` instance's `.Value` property to access the updated value:

# Save a [ref] instance in a variable, pass it, then use .Value to get the 
# updated value.
PS> [ref] $intRef = 0; $null = [int]::TryParse('42', $intRef); $intRef.Value
42

Answer 2

class powerhe11 {

# Constructor
powerhe11() {
}

    [void]AccessChannel(
        [ref]$ichan

    ) {         
         $ichan.value = 0xbeef;
         
         Write-Host("ichan: {0}" -f $ichan.value)
    }

}



[UInt64]$dude = 0

$ser = [gvmuart]::new()

$ser.AccessChannel([ref]$dude);


Write-Host -BackgroundColor Green "DUDE: $dude"