Question

前段时间我更改了Join-Object cmdlet，这似乎导致了一个在我的任何测试中都没有显示的错误。
更改的目标主要是代码最小化并尝试通过准备自定义PSObject并在管道中重复使用来提高性能由于Join-Object cmdlet相当复杂，我创建了一个简化的cmdlet来显示具体问题：
_{（PowerShell版本为：[INFO] Scanning for projects...
[INFO]
[INFO] Using the builder org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder with a thread count of 1
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building FAM.Automation.Selenium 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ FAM.Automation.Selenium ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.6.1:compile (default-compile) @ FAM.Automation.Selenium ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ FAM.Automation.Selenium ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.6.1:testCompile (default-testCompile) @ FAM.Automation.Selenium ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.19.1:test (default-test) @ FAM.Automation.Selenium ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.201 s
[INFO] Finished at: 2018-03-09T19:02:34+08:00
[INFO] Final Memory: 11M/155M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.19.1:test (default-test) on project FAM.Automation.Selenium: Unable to parse configuration of mojo org.apache.maven.plugins:maven-surefire-plugin:2.19.1:test for parameter suiteXmlFiles: Basic element 'suite' must not contain child elements -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginConfigurationException
）}

5.1.16299.248

直接测试输出完全符合我的预期：

Function Test($Count) {
    $PSObject = New-Object PSObject -Property @{Name = $Null; Value = $Null}
    For ($i = 1; $i -le $Count; $i++) {
        $PSObject.Name = "Name$i"; $PSObject.Value = $i
        $PSObject
    }
}

假设我是否将结果分配给变量（例如Test 3 | ft Value Name ----- ---- 1 Name1 2 Name2 3 Name3）并不重要，但确实如此：

$a

所以，除了分享这段经历之外，我想知道这是编程缺陷还是PowerShell bug / quirk？

Answer 1

您的原始方法在概念上确实存在缺陷，因为您多次输出相同的对象，反复修改其属性。

输出中的差异由管道的逐项处理解释：

输出到控制台（通过ft / Format-Table）打印{em>当前状态$PSObject在每次迭代中，它表明一切都很好。
相比之下，捕获变量会在所有迭代完成后反映$PSObject的状态，此时它只包含最后次迭代的值，Name3和3。

您可以验证输出数组$a确实引用了相同的自定义对象三次，如下所示：

[object]::ReferenceEquals($a[0], $a[1]) # $True [object]::ReferenceEquals($a[1], $a[2]) # $True

因此，解决方案是在每次迭代中创建一个独特的[pscustomobject]实例 ：

PSv3 + 提供用于创建自定义对象的语法糖：您可以将哈希表（文字）转换为[pscustomobject]。由于这也每次都会创建一个新实例，因此您可以使用它来简化您的功能：

Function Test($Count) { For ($i = 1; $i -le $Count; $i++) { [pscustomobject] @{ Name = "Name$i"; Value = $i } } }

这是您自己的与PSv2兼容的解决方案：

Function Test($Count) { $Properties = @{} For ($i = 1; $i -le $Count; $i++) { $Properties.Name = "Name$i"; $Properties.Value = $i New-Object PSObject -Property $Properties } }

重用管道的自定义对象时出现意外结果

1 个答案: