FunctionCache.ps1

### all this goes into the begin {} block of a cmdlet

# check and/or set function cache
# scope must be global to remain in memory until the function is called again
# variable will be names "cache_" + name of the function
# initial value will be an empty hashtable, so you can add data nodes as needed in your function
$CacheName = "cache_$($MyInvocation.InvocationName)"
if ( -not ( Get-Variable -Name $CacheName -Scope global -ErrorAction SilentlyContinue ) ) {
    New-Variable -Name $CacheName -Value @{} -Scope global
}

# for ease of use reference the hashtable to a local variable
# since referenced and not copied, all changes to the local variable will
# be replicated in the global cache variable
$Cache = (Get-Variable -Name $CacheName).Value

### usage example

# load data to cache if not there
# HERE IS THE PERFORMANCE GAIN: if the data is already there, you don't need to
# fetch it from the remote system!
if ( -not $Cache.AcceptedDomains ) {
    $Cache.AcceptedDomains = ( Get-AcceptedDomain ).DomainName | Sort-Object
}

function isAcceptedDomain ( [System.Net.Mail.MailAddress]$SmtpAddress ) {
    [array]::BinarySearch($Cache.AcceptedDomains, $SmtpAddress.Host) -ge 0
}