Dew Drop – January 29, 2009 | Alvin Ashcraft's Morning Dew

Dew Drop – January 29, 2009 | Alvin Ashcraft's Morning Dew — Thu, 29 Jan 2009 19:32:59 GMT

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re: PowerShell LINQ: Skip-While

Josh Einstein — Wed, 18 Feb 2009 08:31:41 GMT

Here's a trick to get your lambdas to use the standard $_ convention for current item.

This used to work and I think it still does if the function is a "normal" .ps1 style function:

function Blah([ScriptBlock]$Predicate) {

process { if (&$Predicate) { $_ } }

}

1,2,3 | blah { $_ -eq 3 }

But that no longer works in PowerShell 2.0 CTP 3 when using a .psm1. I still can't quite figure out why but I think it has something to do with the way PowerShell is capturing the variable before calling the function.

So anyway, this does in fact work:

function Blah([ScriptBlock]$Predicate) {

process { if (Invoke-Expression "$Predicate") { $_ } }

}

Notice how the Predicate is being converted back to a string and passed to iex which inherits the $_ variable.

Anyhow, I got sick of using $args[0] for my predicates when everywhere else used $_ so I banged my head against the wall for hours until I figured out a suitable workaround.