Powershell 覆盖赋值和比较运算符

Question

使用 Powershell 5，您现在可以实现自定义类。最终，您会想要开始重载运算符以执行诸如

之类的操作

class Number
{
    [int] $value = 0

    Number() {} # empty constructor

    Number ([int]$somethingElse)
        {$this.value = $somethingElse}
}

$one = [number]::new(1)
$two = [number]::new(2)
$three = $one + $two
if ($three -eq ($one + $two))
    {"3 = 1 + 2"}
else
    {"3 <> 1 + 2 "}

但这似乎没有很好的记录，在 Stack Overflow 上搜索后我找不到如何做到这一点

Answer 1

通常认为您不能在 powershell 中执行此操作。不幸的是，经过几次谷歌搜索和 Stack Overflow 上的搜索，我几乎要放弃了。但后来我在 gist 上发现了this post，结果证明你可以！

考虑到我很难发现，我想为其他人（以及当我很快忘记如何做这件事时的未来自己）提供一个清晰且格式正确的示例

感谢 JFFail 将 this 发布到 Github

您将需要酌情重载这些内容，它们应该是不言自明的，但如果有什么问题，请随时询问

SetValue([int]$newValue)
GetValue()
[boolean] Equals($otherNumber)
[string] ToString() # you can get more advanced by overloading "IConvertible.ToType" but that's a whole can of worms all it's own
static [MyClass] op_Addition   ([MyClass]$first, [MyClass]$second)
static [MyClass] op_Subtraction([MyClass]$first, [MyClass]$second)
static [MyClass] op_Multiply   ([MyClass]$first, [MyClass]$second)
static [MyClass] op_Division   ([MyClass]$first, [MyClass]$second)

对于-gt 和-lt，您需要使用以下内容。请注意，虽然这确实支持-eq，但您可以使用Equals(object) 自行获得它，如上所示，并且不需要从IComparable 继承

class MyClass : System.IComparable 
# requires inheritance from System.IComparable

[int] CompareTo($otherNumber)
# CANNOT declare type in parameter declaration, you'd have to check it later.
# 1 is greater than
# 0 is equal
# -1 is less than
# $null can be returned to indicate invalid comparison

这是一个工作示例

# If you don't need -lt or -gt then you don't have to inherit from System.IComparable
class Number : System.IComparable
{
    [int] $value = 0

    Number() {} # empty constructor

    Number ([int]$somethingElse)
        {$this.value = $somethingElse}

    [void] SetValue ([int]$newValue)
        {$this.value = $newValue}

    [int] GetValue()
        {return $this.value}

    [boolean] Equals($otherNumber)
    {
        if ($this.value -eq $otherNumber.GetValue())
            {return $true}
        else
            {return $false}
    }

    [int] CompareTo($otherNumber)
    {
        if ($this.value -gt $otherNumber.GetValue()) {return 1}
        if ($this.value -eq $otherNumber.GetValue()) {return 0}
        if ($this.value -lt $otherNumber.GetValue()) {return -1}
        return $null
    }

    [string] ToString()
        {return $this.value.ToString()}

    static [Number] op_Addition ([Number]$first, [Number]$second)
        {return [Number]::new($first.GetValue() + $second.GetValue())}

    static [Number] op_Subtraction([Number]$first, [Number]$second)
        {return [Number]::new($first.GetValue() - $second.GetValue())}

    static [Number] op_Multiply([Number]$first, [Number]$second)
        {return [Number]::new($first.GetValue() * $second.GetValue())}

    static [Number] op_Division([Number]$first, [Number]$second)
        {return [Number]::new($first.GetValue() / $second.GetValue())}
}

# Very Basic Unit Tests
$firstNumber = [Number]::new(8)
$secondNumber = [Number]::new(12)
$thirdNumber = [Number]::new(8)

if ($firstNumber -eq $secondNumber)
    {Write-Output ("{0} == {1}" -F $firstNumber, $secondNumber)}
else
    {Write-Output ("{0} <> {1}" -F $firstNumber, $secondNumber)}

if ($firstNumber -eq $thirdNumber)
    {Write-Output ("{0} == {1}" -F $firstNumber, $thirdNumber)}
else
    {Write-Output ("{0} <> {1}" -F $firstNumber, $thirdNumber)}

switch ($true)
{
    ($firstNumber -gt $secondNumber) {Write-Output ("{0} > {1}" -F $firstNumber, $secondNumber)}
    ($firstNumber -eq $secondNumber) {Write-Output ("{0} == {1}" -F $firstNumber, $secondNumber)}
    ($firstNumber -lt $secondNumber) {Write-Output ("{0} < {1}" -F $firstNumber, $secondNumber)}
}

$fourthNumber = $firstNumber + $secondNumber
Write-Output ("{0} = {1} + {2}" -F $fourthNumber, $firstNumber, $secondNumber)

$fifthNumber = $secondNumber - $thirdNumber
Write-Output ("{0} = {1} - {2}" -F $fifthNumber, $secondNumber, $thirdNumber)

$sixthNumber = $firstNumber * $secondNumber
Write-Output ("{0} = {1} * {2}" -F $sixthNumber, $firstNumber, $secondNumber)

$seventhNumber = $sixthNumber / $firstNumber
Write-Output ("{0} = {1} / {2}" -F $seventhNumber, $sixthNumber, $firstNumber)

这是输出

> 8 <> 12
> 8 == 8
> 8 < 12
> 20 = 8 + 12
> 4 = 12 - 8
> 96 = 8 * 12
> 12 = 96 / 8