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PowerShell by default enumerates (unrolls) collections[1] when outputting them to the pipeline: that is, instead of outputting the collection itself, its elements are output, one by one.
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电源外壳将管道中的所有输出对象收集到平面数组中（类型[object[]]，即一个数组，其元素可以是任何类型（System.Object)), if 两个或更多输出对象（asingle对象被收集本身).
因此，即使输出multiple数组创建一个single，默认情况下平面输出数组，这是级联这些数组。
一个更简单的例子：
# Output 2 2-element arrays.
PS> 1..2 | % { @(1, 2) } | Measure-Object | % Count
4 # i.e., @(1, 2, 1, 2).Count
为了生产nested数组，你必须抑制枚举，可以通过两种方式实现：
- 最简单的选择：将输出数组包装在辅助瞬态单元阵列这样当 PowerShell 枚举 aux.数组其唯一的元素 - 原始数组 - 是输出作为一个整体, as a 单个对象。这可以通过以下方式实现一元形式
, the 数组构造函数（“逗号”）运算符:
# Use unary , to wrap the RHS in a transient single-element array,
# which ensures that @(1, 2) is output *as a whole*.
PS> 1..2 | % { , @(1, 2) } | Measure-Object | % Count
2 # i.e., @(@(1, 2), @(1, 2)).Count
- 替代方案，使用
Write-Output -NoEnumerate（PSv4+；这更慢，但概念上更明确）：
PS> 1..2 | % { Write-Output -NoEnumerate @(1, 2) } | Measure-Object | % Count
2 # i.e., @(@(1, 2), @(1, 2)).Count
Note:
- While use of
@(...) is not strictly necessary to create array literals (as used above) - for literals, separating elements with , is sufficient[2] - you still need @(...) to ensure that output from enclosed expressions or commands is treated as an array, in case only a single object happens to be output.
[1] Specifically, types that implement the System.Collections.IEnumerable interface or its generic counterpart are enumerated, but there are a few exceptions, notably strings and dictionaries. See the bottom section of this answer for details.
[2] E.g., 1, 2 creates a two-element array. In the case of nesting such an array via unary ,, you do need an enclosure, however, to clarify precedence, for which the general-purpose (...) (grouping operator) would suffice: , (1, 2) - though you may prefer , @(1, 2) for conceptual clarity.
