Duck typing for indexed iteratables in Powershell

Question

Instead of piping over collections, it's sometimes more convenient to procedurally loop through them. And to avoid differentiating between $_ and $_.Key/$_.Value depending on input, a more consistent key/value handling would be nice:

ForEach-KV $object { Param($k, $v); do-stuff }

However a common type probing has its drawbacks:

#-- iterate over dicts/objects/arrays using scriptblock with Param($k,$v)
function ForEach-KV {
    Param($var, $cb, $i=0)
    switch ($var.GetType().Name) {
        Array          { $var | % { $cb.Invoke($i++, $_) } }
        HashTable      { $var.Keys | % { $cb.Invoke($_, $var[$_]) } }
       "Dictionary``2" { $var.Keys | % { $cb.Invoke($_, $var.Item($_)) } }
        PSobject       { $var.GetIterator() | % { $cb.Invoke($_.Key, $_.Value) } }
        PSCustomObject { $var.GetIterator() | % { $cb.Invoke($_.Key, $_.Value) } }
        default        { $cb.Invoke($i++, $_) }
    }
}

Apart from that one irritating type name, there's a bit much duplication here. Which is why I was looking around for duck typing in Powershell.

For hashes and objects, it's easiest/obvious to probe for .getIterator or .getEnumerator (never couldn't quite remember which belongs to which anyway):

switch ($_) {
    { $_.GetEnumerator }  { do-loopy }
    { $_.GetIterator }    { do-otherloopy }

But now I'm not quite sure what to do about arrays here. There's not that one behaviour indicator in [array]s methods that really sticks out.

• .Get() does seem unique (at least not a method in HashTables or PSObjects), but sounds a bit too generic even for type guessing
• .Add() might as well be an integer method(?)
• .GetUpperBound() etc. come off as a bit too specific already.

So, is there a standard method that says "arrayish", preferrably something that's shared among other numerically-indexed value collections?

Answer 1

If you want to match only arrays:

PS> $x = 1..10
PS> $x.GetType().IsArray
True

or you can check there is integer indexer:

(Get-Member -InputObject $x -Name 'Item' -MemberType 'ParameterizedProperty').Definition -match '\(int index\)'