在PowerShell中调用泛型静态方法

可以调用泛型方法,请参阅文章 Invoking Generic Methods on Non-Generic Classes in PowerShell .

这并不简单,你需要使用 MakeGenericMethod 功能。如果方法没有重写,则非常简单,如果有重写,则会变得更加困难。

以防万一,从那里复制粘贴的代码:

## Invoke-GenericMethod.ps1 
## Invoke a generic method on a non-generic type: 
## 
## Usage: 
## 
##   ## Load the DLL that contains our class
##   [Reflection.Assembly]::LoadFile("c:\temp\GenericClass.dll")
##
##   ## Invoke a generic method on a non-generic instance
##   $nonGenericClass = New-Object NonGenericClass
##   Invoke-GenericMethod $nonGenericClass GenericMethod String "How are you?"
##
##   ## Including one with multiple arguments
##   Invoke-GenericMethod $nonGenericClass GenericMethod String ("How are you?",5)
##
##   ## Ivoke a generic static method on a type
##   Invoke-GenericMethod ([NonGenericClass]) GenericStaticMethod String "How are you?"
## 

param(
    $instance = $(throw "Please provide an instance on which to invoke the generic method"),
    [string] $methodName = $(throw "Please provide a method name to invoke"),
    [string[]] $typeParameters = $(throw "Please specify the type parameters"),
    [object[]] $methodParameters = $(throw "Please specify the method parameters")
    ) 

## Determine if the types in $set1 match the types in $set2, replacing generic
## parameters in $set1 with the types in $genericTypes
function ParameterTypesMatch([type[]] $set1, [type[]] $set2, [type[]] $genericTypes)
{
    $typeReplacementIndex = 0
    $currentTypeIndex = 0

    ## Exit if the set lengths are different
    if($set1.Count -ne $set2.Count)
    {
        return $false
    }

    ## Go through each of the types in the first set
    foreach($type in $set1)
    {
        ## If it is a generic parameter, then replace it with a type from
        ## the $genericTypes list
        if($type.IsGenericParameter)
        {
            $type = $genericTypes[$typeReplacementIndex]
            $typeReplacementIndex++
        }

        ## Check that the current type (i.e.: the original type, or replacement
        ## generic type) matches the type from $set2
        if($type -ne $set2[$currentTypeIndex])
        {
            return $false
        }
        $currentTypeIndex++
    }

    return $true
}

## Convert the type parameters into actual types
[type[]] $typedParameters = $typeParameters

## Determine the type that we will call the generic method on. Initially, assume
## that it is actually a type itself.
$type = $instance

## If it is not, then it is a real object, and we can call its GetType() method
if($instance -isnot "Type")
{
    $type = $instance.GetType()
}

## Search for the method that:
##    - has the same name
##    - is public
##    - is a generic method
##    - has the same parameter types
foreach($method in $type.GetMethods())
{
    # Write-Host $method.Name
    if(($method.Name -eq $methodName) -and
    ($method.IsPublic) -and
    ($method.IsGenericMethod))
    {
        $parameterTypes = @($method.GetParameters() | % { $_.ParameterType })
        $methodParameterTypes = @($methodParameters | % { $_.GetType() })
        if(ParameterTypesMatch $parameterTypes $methodParameterTypes $typedParameters)
        {
            ## Create a closed representation of it
            $newMethod = $method.MakeGenericMethod($typedParameters)

            ## Invoke the method
            $newMethod.Invoke($instance, $methodParameters)

            return
        }
    }
}

## Return an error if we couldn't find that method
throw "Could not find method $methodName"

正如@Athari所说,调用MyMethod的最简单方法是使用MakeGenericMethod。由于他实际上并没有演示如何做到这一点,下面是一个经过验证的工作代码示例:

$obj = New-Object Sample

$obj.GetType().GetMethod("MyMethod").MakeGenericMethod([String]).Invoke($obj, "Test Message")
$obj.GetType().GetMethod("MyMethod").MakeGenericMethod([Double]).Invoke($obj, "Test Message")

有输出

Generic type is System.String with argument Test Message
Generic type is System.Double with argument Test Message

这是PowerShell的一个限制,不能直接在PowerShell V1或V2 AFAIK中完成。

顺便说一句,你的泛型方法并不是真正的泛型方法。不应该是:

public static string MyMethod<T>(T anArgument)
{ 
   return string.Format( "Generic type is {0} with argument {1}", 
                         typeof(T), anArgument.ToString()); 
} 

如果您拥有此代码并希望从PowerShell中使用它,请避免使用泛型方法或编写非泛型C包装器方法。

好消息是,PowerShell v3在绑定到泛型方法(并具体化它们)方面做得更好你通常不需要做任何特别的事情,只要像平常一样调用它。我不能指定所有现在运行的标准,但是在我的经验中,某些通用参数的情况甚至需要在PultSeaveV4(可能是存在或重载或类似的情况下)。

类似地,我有时也很难将泛型参数传递给方法。。。例如通过 Func<T1, T2, TResult> 参数。

对我来说,解决这个问题的一个方法比MakeGenericMethod或其他方法简单得多,就是直接在我的脚本中放入一个快速的C包装类,然后让C整理所有的泛型映射。。。

下面是这种方法的一个示例,它将 Enumerable.Zip 方法。在这个例子中,我的c类根本不是泛型的,但严格来说这并不是必要的。

Add-Type @'
using System.Linq;
public class Zipper
{
    public static object[] Zip(object[] first, object[] second)
    {
        return first.Zip(second, (f,s) => new { f , s}).ToArray();
    }
}
'@
$a = 1..4;
[string[]]$b = "a","b","c","d";
[Zipper]::Zip($a, $b);

这会产生:

 f s
 - -
 1 a
 2 b
 3 c
 4 d

我相信有更好的PowerShell方法来“压缩”两个数组,但你明白了。我在这里回避的真正挑战是有一个硬编码(在C类中)的第三个参数 Zip 所以我不必想办法 函数<T1,T2,结果> (也许还有一个超级地狱的方法可以做到这一点?).

快速方式,如果没有名称冲突:

[Sample]::"MyMethod"("arg")