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SendETHToThisAddress

Reputation: 3704

PowerShell - array of type HashSet

I am trying to create an array of HashSets but it always comes out as simply a HashSet. Here is a test script I made:

$arrHashSets = @();

$hs = New-Object System.Collections.Generic.HashSet[string];
$hs2 = New-Object System.Collections.Generic.HashSet[string];

$hs.Add("A");
$hs.Add("B");
$hs.Add("C");

$hs2.Add("A");
$hs2.Add("B");
$hs2.Add("C");

$arrHashSets += $hs;
$arrHashSets += $hs2;

Expected result:

$arrHashSets = [
    {"A", "B", "C"},
    {"A", "B", "C"}
]

Actual result:

$arrHashSets = {"A", "B", "C"}

I tried doing it a few different ways but $arrHashSets always comes out as simply a HashSet rather than an array of type HashSet. What am I doing wrong?

Upvotes: 1

Views: 769

Answers (1)

mklement0
mklement0

Reputation: 437638

Replace:

$arrHashSets += $hs
$arrHashSets += $hs2

with:

$arrHashSets = $hs, $hs2

If you do need to build up an array(-like data structure) iteratively:

$lstHashSets = [System.Collections.Generic.List[object]]::new()
foreach ($thisHs in $hs, $hs2) {
  $lstHashSets.Add($thisHs)
}

Note: For simplicity the generic list is [object]-typed here, but you could more strictly type it as [System.Collections.Generic.List[System.Collections.Generic.HashSet[string]]].

However, creating an array / list explicitly isn't strictly needed, given that you can use a statement such as foreach loop as an expression whose multiple outputs PowerShell implicitly captures in an array for you:

$arrHashSets = @(
  foreach ($thisHs in $hs, $hs2) {
    , $thisHs
  }
)

Note:

  • @(...), the array-subexpression operator is necessary to ensure that an array is also constructed in the event that the foreach loop happens to output only a single object.

  • The unary form of ,, the array constructor operator is used to in effect ensure that each hash set is output as a whole. By default, PowerShell would enumerate the hash set's entries, i.e. output them one by one - see this answer for more information.

As for what you tried:

Using += to "extend" an array:

  • is generally to be avoided due to its inefficiency: a new array must be created behind the scenes every time - see this answer.

  • "adds" to the existing array by appending the elements of the RHS, if it is an enumerable, rather than appending the RHS as a whole. Thus, the hash set is enumerated and its elements become direct elements of the resulting, flat array.

Upvotes: 3

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