Powershell 'x or y' assignment

Question

There are several languages that provide either a defaulting or logical or mechanism for assignment:

a = b || c;
a = b or c
a="${b:-$c}"
a = b ? b : c;

So far the only equivalent I've found in Powershell Core is the exceedingly verbose:

$a = if ($b) { $b } else { $c }

which in some cases has to become

$a = if ($b -ne $null) { $b } else { $c }

Is there a better alternative [edit:] which doesn't sacrifice readability?

Answer 1

There's no || short-circuit operator in PowerShell assignments, and nothing equivalent to Perl's // "defined-or" operator - but you can construct a simple null coalesce imitation like so:

function ?? {
  param(
    [Parameter(Mandatory=$true,ValueFromRemainingArguments=$true,Position=0)]
    [psobject[]]$InputObject,

    [switch]$Truthy
  )

  foreach($object in $InputObject){
    if($Truthy -and $object){
      return $object
    }
    elseif($object -ne $null){
      return $object
    }
  }
}

Then use like:

$a = ?? $b $c

or, if you want to just have return anything that would have evaluated to $true like in your first example:

$a = ?? $b $c -Truthy

Answer 2

So a simple method for reducing this:

$a = if ($b -ne $null) { $b } else { $c }

Would be to use the fact that true and false are just one or zero and could be used as an array index like so:

$a =  @($c, $b)[$b -ne $null]