具有无限深度的哈希表。为什么？如何避免？

Question

当我使用 $emptyHashTable 变量创建一个空哈希表时，它似乎生成了一个无限深度的哈希表。想不通为什么。
当我使用 @{} 时它工作正常。

代码示例

cls

$L1     = "L1"
$emptyHashTable = @{}

# Correct, hashtable contains 1 sub-hashtable
$proj1       = @{}
$proj1."$L1" = @{}

# Wrong, endless hashtable depth
$proj2       = @{}
$proj2."$L1" = $emptyHashTable

# Wrong, endless hashtable depth
$proj3       = $emptyHashTable
$proj3."$L1" = @{}

# Wrong, endless hashtable depth
$proj4       = $emptyHashTable
$proj4."$L1" = $emptyHashTable

Write-Host
Write-Host "proj1"
Write-Host "Level 0: " $proj1.GetType()
Write-Host "Level 1: " $proj1.L1.GetType()
Write-Host "Level 2: " $proj1.L1.L1.GetType() # Will generate error: You cannot call a method on a null-valued expression.
Write-Host
Write-Host "proj2"
Write-Host "Level 0: " $proj2.GetType()
Write-Host "Level 1: " $proj2.L1.GetType()
Write-Host "Level 2: " $proj2.L1.L1.GetType()
Write-Host "Level 3: " $proj2.L1.L1.L1.GetType()
Write-Host "Level 4: " $proj2.L1.L1.L1.L1.GetType()
Write-Host
Write-Host "proj3"
Write-Host "Level 0: " $proj3.GetType()
Write-Host "Level 1: " $proj3.L1.GetType()
Write-Host "Level 2: " $proj3.L1.L1.GetType()
Write-Host "Level 3: " $proj3.L1.L1.L1.GetType()
Write-Host "Level 4: " $proj3.L1.L1.L1.L1.GetType()
Write-Host
Write-Host "proj4"
Write-Host "Level 0: " $proj4.GetType()
Write-Host "Level 1: " $proj4.L1.GetType()
Write-Host "Level 2: " $proj4.L1.L1.GetType()
Write-Host "Level 3: " $proj4.L1.L1.L1.GetType()
Write-Host "Level 4: " $proj4.L1.L1.L1.L1.GetType()

结果

proj1
Level 0:  System.Collections.Hashtable
Level 1:  System.Collections.Hashtable
You cannot call a method on a null-valued expression.
At D:\Xandorra\SQL\bmsHashTableTest.ps1:25 char:1
+ Write-Host "Level 2: " $proj1.L1.L1.GetType() # Will generate error: You cannot  ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull


proj2
Level 0:  System.Collections.Hashtable
Level 1:  System.Collections.Hashtable
Level 2:  System.Collections.Hashtable
Level 3:  System.Collections.Hashtable
Level 4:  System.Collections.Hashtable

proj3
Level 0:  System.Collections.Hashtable
Level 1:  System.Collections.Hashtable
Level 2:  System.Collections.Hashtable
Level 3:  System.Collections.Hashtable
Level 4:  System.Collections.Hashtable

proj4
Level 0:  System.Collections.Hashtable
Level 1:  System.Collections.Hashtable
Level 2:  System.Collections.Hashtable
Level 3:  System.Collections.Hashtable

我正在使用 Powershell 4.0
我的 $PSVersionTable:

Name                           Value                                                               
----                           -----                                                               
PSVersion                      4.0                                                                 
WSManStackVersion              3.0                                                                 
SerializationVersion           1.1.0.1                                                             
CLRVersion                     4.0.30319.34014                                                     
BuildVersion                   6.3.9600.17400                                                      
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0}                                                
PSRemotingProtocolVersion      2.2

Answer 1

您忽略了一个事实，即对象是按引用传递的，而不是按值传递的。

正是您的测试结构使这些结果蒙上了阴影。运行每个人 $projX 在自己的 powershell 实例中分配，没有运行其他实例，它应该按预期工作。

例如，当你写：

$proj2."$L1" = $emptyHashTable

$proj3       = $emptyHashTable
$proj3."$L1" = @{}

您已将 $proj2.L1 设置为 对 $emptyHashTable 的引用。因此，您还将 $proj3 设置为 reference 到 $proj2.L1，从而成为 $emptyHashTable。这意味着 $proj3.L1 = @{} 与 $proj2.L1.L1 = @{} 相同，依此类推。

Answer 2

这似乎是 Powershell v4 中的错误。
同样的代码在Powershell v5中运行时，不会出现无限深度

具有无限深度的哈希表。为什么？如何避免？

HashTable with endless depth. Why? How to avoid?

powershell

powershell-4.0