Change the evaluator within a switch statement - powershell

Question

Is there a way, in a 'switch' to modify the variable you are evaluating on, and get it to change the match?
$var = "a"
switch ($var){
"a" {Write-Host "1st match for 'a'"}
"b" {Write-Host "1st match for 'b'"}
"a" {Write-Host "2nd match for 'a'"; $var = "b" ; continue}
"b" {Write-Host "2st match for 'b'"}
}
I would love to be able to get the above to match:
1st match for 'a'
2nd match for 'a'
2nd match for 'b'
$Destination = "vmstores:\vcsa#443\Training\Local-B\David" #is a param of my function, which could be a bunch of different types of object.
$DestinationType = $Destination.GetType().Name
switch ($DestinationType){
"String" {
if ((Test-Path $Destination) -eq $true){
if ((Get-Item $Destination).GetType().Name -eq "DatastoreFolderImpl"){
$DestinationType = "DatastoreFolderImpl"
if ((Test-Path $Destination.Insert($Destination.Length,"\").Insert(($Destination.Length)+1,$SourceVMXShort)) -eq $true){
Write-Warning "Destination File exists..."
$DestinationExists = $true
}
}
elseif ((Get-Item $Destination).GetType().Name -eq "DatastoreFileImpl"){
$DestinationType = "DatastoreFileImpl"
Write-Warning "Destination File exists..."
$DestinationExists = $true
}
}
; continue
}
"DirectoryInfo" {
if ((Test-Path $Destination.Insert($Destination.Length,"\").Insert(($Destination.Length)+1,$SourceVMXShort)) -eq $true){
Write-Warning "Destination File exists..."
$DestinationExists = $true
}
; break
}
"FileInfo" {
if ((Test-Path $Destination) -eq $true){
Write-Warning "Destination File exists..."
$DestinationExists = $true
}
; break
}
"DatastoreFileImpl" {
if ((Test-Path $Destination) -eq $true){
Write-Warning "Destination File exists..."
$DestinationExists = $true
}
; break
}
"DatastoreFolderImpl" {
if ((Test-Path $Destination.Insert($Destination.Length,"\").Insert(($Destination.Length)+1,$SourceVMXShort)) -eq $true){
Write-Warning "Destination File exists..."
$DestinationExists = $true
}
; break
}
"NasDatastoreImpl" {
New-PSDrive -Name "DestMount" -Root \ -PSProvider VimDatastore -Datastore $Destination | Out-Null
if ((Test-Path ("DestMount:").insert(10,"\").Insert(11,$SourceVMXShort)) -eq $true){
Write-Warning "Destination File exists..."
$DestinationExists = $true
}
$Destination = ("DestMount:").insert(10,"\")
; break
}
"VMFSDatastoreImpl" {
New-PSDrive -Name "DestMount" -Root \ -PSProvider VimDatastore -Datastore $Destination | Out-Null
if ((Test-Path ("DestMount:").insert(10,"\").Insert(11,$SourceVMXShort)) -eq $true){
Write-Warning "Destination File exists..."
$DestinationExists = $true
}
$Destination = ("DestMount:").insert(10,"\")
; break
}
}
As you can see, it would be more elegant if i could update the $DestinationType so i could re-use the statement in the other switch blocks, rather than the extra 'ifs'

Answer 1

While I don't think you can change the switch statements variable mid check, you can do nested switch statements. This code gives your requested output:
$var = "a"
switch ($var){
"a" {Write-Host "1st match for 'a'"}
"b" {Write-Host "1st match for 'b'"}
"a" {Write-Host "2nd match for 'a'"
$var = "b"
switch ($var) {
"b" {Write-Host "2st match for 'b'"}
} #End sub-switch
} #End "A" check
} #End Primary switch
Now, I'm not sure what your overall goal is, there might be better ways to do this with functions and such.
Edit after updated question and comments:
From looking at the updated code, you can pull the one if statement that sets $DestinationExists = $true. You might be able to reorganize your if statements so they only show up once. Unfortunately, there is no way to get the switch statement to change the variable mid-switch. From your comment, maybe you can add an extra parameter that will dictate the type, so you can us one large switch statement based off the type. Something like this:
switch ($DataType) {
"String" {<#Things to do if string#>}
"OtherTypes" {<#Continue like this#>}
}#End Switch ($DataType)
I think at that point though, I would start using Parameter Sets. Here is a blog describing about Parameter Sets

Answer 2

Here is a somewhat convoluted way to do it. Note that the example code is similar but not the same as the code in OP.
add-type #"
using System;
using System.Collections;
using System.Collections.ObjectModel;
using System.Management.Automation;
public class PSVarEnumeration : IEnumerable
{
private ScriptBlock _getterScript;
public PSVarEnumeration(ScriptBlock getterScript)
{
_getterScript = getterScript;
}
IEnumerator IEnumerable.GetEnumerator()
{
return (IEnumerator) GetEnumerator();
}
public PSVarEnumerator GetEnumerator()
{
return new PSVarEnumerator(_getterScript);
}
}
public class PSVarEnumerator : IEnumerator
{
private ScriptBlock _getterScript;
bool areDone = false;
// position isn't used for anything
int position = -1;
public PSVarEnumerator(ScriptBlock getterScript)
{
_getterScript = getterScript;
}
public bool MoveNext()
{
if (!areDone) {
if (Current != null) {
position++;
return true;
} else {
areDone = true;
return false;
}
} else {
return false;
}
}
public void Reset()
{
position = -1;
areDone = false;
}
object IEnumerator.Current
{
get
{
return Current;
}
}
public Object Current
{
get
{
Collection<PSObject> results = _getterScript.Invoke();
return results[0];
}
}
}
"#
$mySwitcher ="a"
$mySwitcherScript = {$mySwitcher}
$var = new PSVarEnumeration ( $mySwitcherScript)
switch ($var){
"a" {Write-Host "1st match for 'a'"}
"b" {Write-Host "1st match for 'b'"}
"a" {Write-Host "2nd match for 'a'"; $mySwitcher = "b" ; continue}
"b" {Write-Host "2nd match for 'b'"; $mySwitcher = $null}
}
<#
Output I get is:
1st match for 'a'
2nd match for 'a'
1st match for 'b'
2nd match for 'b'
#>