Classic foreach loops are the fastest loop available but they come with a severe limitation. Foreach loops do not support streaming. You need to always wait for the entire foreach loop to finish before you can start processing the results.
Here are some example illustrating this. With the code below, you have to wait a long time until you “see” the results:
$result = foreach ($item in $elements) { "processing $item" # simulate some work and delay Start-Sleep -Milliseconds 50 } $result | Out-GridView
You cannot pipe the results directly. The following code produces a syntax error:
$elements = 1..100 Foreach ($item in $elements) { "processing $item" # simulate some work and delay Start-Sleep -Milliseconds 50 } | Out-GridView
You could use $() to enable piping, but you would still have to wait for the loop to finish before the results are piped in one big chunk:
$elements = 1..100 $(foreach ($item in $elements) { "processing $item" # simulate some work and delay Start-Sleep -Milliseconds 50 }) | Out-GridView
Here is a little-known trick that adds real-time streaming to foreach: simply use a script block!
$elements = 1..100 & { foreach ($item in $elements) { "processing $item" # simulate some work and delay Start-Sleep -Milliseconds 50 }} | Out-GridView
Now you “see” the results as they are produced, and enjoy real-time streaming.
Of course, you could as well abandon foreach in the first place, and use the ForEach-Object pipeline cmdlet instead:
$elements = 1..100 $elements | ForEach-Object { $item = $_ "processing $item" # simulate some work and delay Start-Sleep -Milliseconds 50 } | Out-GridView
However, ForEach-Object is much slower than the foreach keyword, and there are cases where you simply can’t use ForEach-Object. For example, in a lot of database code, your code needs to check for end-of-file flags and reads records one by one which exclude ForEach-Object as an option.
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