I've found some interesting behaviour in PowerShell Arrays, namely, if I declare an array as:
$array = @()
And then try to add items to it using the $array.Add("item") method, I receive the following error:
Exception calling "Add" with "1" argument(s): "Collection was of a fixed size."
However, if I append items using $array += "item", the item is accepted without a problem and the "fixed size" restriction doesn't seem to apply.
Why is this?
This question is related to
arrays
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When using the $array.Add()-method, you're trying to add the element into the existing array. An array is a collection of fixed size, so you will receive an error because it can't be extended.
$array += $element creates a new array with the same elements as old one + the new item, and this new larger array replaces the old one in the $array-variable
You can use the += operator to add an element to an array. When you use it, Windows PowerShell actually creates a new array with the values of the original array and the added value. For example, to add an element with a value of 200 to the array in the $a variable, type:
$a += 200
Source: about_Arrays
+= is an expensive operation, so when you need to add many items you should try to add them in as few operations as possible, ex:
$arr = 1..3 #Array
$arr += (4..5) #Combine with another array in a single write-operation
$arr.Count
5
If that's not possible, consider using a more efficient collection like List or ArrayList (see the other answer).
The most common idiom for creating an array without using the inefficient += is something like this, from the output of a loop:
$array = foreach($i in 1..10) {
$i
}
$array
If you want a dynamically sized array, then you should make a list. Not only will you get the .Add() functionality, but as @frode-f explains, dynamic arrays are more memory efficient and a better practice anyway.
And it's so easy to use.
Instead of your array declaration, try this:
$outItems = New-Object System.Collections.Generic.List[System.Object]
Adding items is simple.
$outItems.Add(1)
$outItems.Add("hi")
And if you really want an array when you're done, there's a function for that too.
$outItems.ToArray()
Source: Stackoverflow.com