Powershell 5 类和单例

Question

是否有使用 PowerShell 5.0 中的类构造创建单例类的正确/最佳/任何方法？我试过这样的事情:

class ScannerGeometry
{
    [int] $EEprom;              # read eeprom
    # ....

    ScannerGeometry()
    {
        # ... fetch calibration from instrument
    }

    [ScannerGeometry] Instance() {
        if ($this -eq $null)
        {
            $this = [ScannerGeometry]::new()
        }
        return $this
    }
}

并将其分配给以下内容:

$scanner = [ScannerGeometry]::Instance()

唉，我收到运行时错误 Method invocation failed because [ScannerGeometry] does not contain a method named 'Instance'.
另外，可以在 PS5 类中将构造函数(或任何其他方法)设为私有(private)吗？

Answer 1

您的方法是这样可见的，因为它不是静态的:

[ScannerGeometry]::new() | set x
PS C:\Work> $x | gm


   TypeName: ScannerGeometry

Name        MemberType Definition
----        ---------- ----------
Equals      Method     bool Equals(System.Object obj)
GetHashCode Method     int GetHashCode()
GetType     Method     type GetType()
Instance    Method     ScannerGeometry Instance()
ToString    Method     string ToString()
EEprom      Property   int EEprom {get;set;}

您需要使用关键字static .在那种情况下 $this无效，因此您必须稍微更改代码。这是代码:

class ScannerGeometry
{
    [int] $EEprom;              # read eeprom


    static [ScannerGeometry] Instance() {
          return [ScannerGeometry]::new()
    }
}

编辑

好的，这是工作代码:

class ScannerGeometry
{
    [int] $EEprom              # read eeprom

    static [ScannerGeometry] $instance


    static [ScannerGeometry] GetInstance() {
          if ([ScannerGeometry]::instance -eq $null) { [ScannerGeometry]::instance = [ScannerGeometry]::new() }
          return [ScannerGeometry]::instance
    }
}

$s = [ScannerGeometry]::GetInstance()