Missing property name after reference operator - powershell

Question

I have a map, that is originally c++ code, file read, and parsed into a map. The original code was an enum, and didn't have values for all items. $fileContent:
enum{
Error_A = 110,
Error_B,
Error_C,
Error_D,
Error_E,
Error_F,
Error_G = 118,
...
};
I have read the file contents and put it in a map like this (works fine):
function Get-Contents_b{
[cmdletbinding()]
Param ([string]$fileContent)
#Error_AA = 20
# create an ordered hashtable to store the results
$errorMap = [ordered]#{}
# process the lines one-by-one
switch -Regex ($fileContent -split '\r?\n') {
'^[\s]*([\w]+)[\s=]*([-\d]*)' { # Error...=12345
$key,$value = ($matches[1,2])|ForEach-Object Trim
$errorMap[$key] = $value
}
}
...
Then I want to iterate over the map, and for the ones with enum values dependent on single digit increase from the previous, I want to assign the value of the previous value plus one. I'm trying to do that below, but getting the $previousKey, using $key-1, and then getting the value from that, is giving the error shown in the comment.
foreach ($key in $errorMap.$keys)
{
$previousKey = $errorMap.[($key-1)] #missing property name after the reference operator
Write-Host $errorMap.$previousKey
if(($errorMap.$key).Value = "")
{
$errorMap.$key.Value = $errorMap.$previousKey.Value + 1
}
}
Any ideas how to fix this or get the previous value and assign the next empty value the previous value plus one?
This is with powershell 5.1 and VSCode.

Answer 1

You're mistakenly mixing member (property) access via the . operator with indexed access via [...] - you must use one or the other.
However, what you want is positional access to your keys (which only works with an ordered hashtable):
foreach ($keyIndex in 0..($errorMap.Count-1))
{
if ('' -eq $errorMap[$keyIndex]) {
$previousValue = $errorMap[$keyIndex - 1]
Write-Host $previousValue
$errorMap[$keyIndex] = 1 + $previousValue
}
}

Answer 2

Why not create the values in your Hashtable straight away instead of filling the empties afterwards?
function Get-Contents_b{
[cmdletbinding()]
Param ([string]$fileContent)
# create an ordered hashtable to store the results
$errorMap = [ordered]#{}
$currentValue = 0
# process the lines one-by-one
switch -Regex ($fileContent -split '\r?\n') {
'^\s+(\w+)\s*[,=]'{
$key, $value = ($_ -split '[,=]', 2).Trim()
if ([string]::IsNullOrWhiteSpace($value)) { $value = $currentValue }
$errorMap[$key] = [int]$value
$currentValue = [int]$value + 1
}
}
# return the map
$errorMap
}
Get-Contents_b $enum
Output:
Name Value
---- -----
Error_A 110
Error_B 111
Error_C 112
Error_D 113
Error_E 114
Error_F 115
Error_G 118