Control statements in assignment RHS #231

Hi Steve, thanks for reporting!

Do you know if those conditionals, loops, and exceptions are available in any arbitrary expression?

Like can I do this with a try/catch?

if (2 * try { Get-Thing } catch { 4 } -gt $sentinel )
{ echo Foo }

The OP's pattern for if is seen in the official docs in Assignment Operators:

You can also assign the value created by a statement to a variable, as in the following example:

$a = if ($b -lt 0) { 0 } else { $b }

This example assigns zero to the $a variable if the value of $b is less than zero. It assigns the value of $b to $a if the value of $b isn't less than zero.

And as an example, not itself documented at foreach:

      $filesToProcess = if ($_ -is [System.IO.FileSystemInfo]) {
        $_
      } else {
        Get-Item -Path $Path
      }

I think I've found the real documentation for this at Statement values. These can get crazy:

$i = 1
$v = while ($i -le 5) {
    $i                   # $i is written to the pipeline
    if ($i -band 1) {
        "odd"            # conditionally written to the pipeline
    }
    ++$i                 # not written to the pipeline
}
# $v is object[], Length 8, value 1,"odd",2,3,"odd",4,5,"odd"

Does this mean that technically every statement is an expression? Including function and class definitions?

As usual, PowerShell is more complicated.

# legal, $foo is 4 (= 0 + 4)
$foo =     try { Get-Thing } catch { 0 } + 4

# crashes
$foo = 4 + try { Get-Thing } catch { 0 }

# compiles, but unclear what $foo becomes
$foo = function Name { 5; Write-Host 6; return 7 }

I think we move exceptions, loops, flow, and conditionals from statements to expressions-without-commands and let the user sort it out if they try to add 4 + try {....