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PSFHashtables

Synopsis​

PSFramework Hashtables - [PsfHashtable] - are an extension / improvement over the default [Hashtable]. They can do everything a regular hashtable can do, but they can also offer alternative options on what to do, when asking for a key not already included in the hashtable.

Description​

The [PsfHashtable] data-type was added as a means to make hashtables more powerful and flexible, in many cases replacing the need for switch-statements. This can help simplify the code layout significantly.

Example: The simple hashtable

$organizations = @{
    LondonHR = 'London'
    LondonSales = 'London'
    LondonDev = 'London'
    NewYorkHR = 'New York'
    NewYorkSales = 'New York'
    NewYorkDev = 'New York'
}

$users | Select-Object Name, Mail, @{
    Name = 'Users'
    Expression = {
        if ($organizations[$_.Organization]) {
            $organizations[$_.Organization]
        }
        else { $_.Organization}
    }
}

Example: PsfHashtable

$organizations = [PsfHashtable]@{
    LondonHR = 'London'
    LondonSales = 'London'
    LondonDev = 'London'
    NewYorkHR = 'New York'
    NewYorkSales = 'New York'
    NewYorkDev = 'New York'
}
# If key not known: Return key
$organizations.EnablePassthru()

$users | Select-Object Name, Mail, @{
    Name = 'Users'
    Expression = { $organizations[$_.Organization] }
}

Special Features​

So, after luring you in with a simple example, what all can the [PsfHashtable] do for you?

PassThru​

As shown in the previous example, a [PsfHashtable] can be configured to pass through the key, if it is not yet known:

$mapping = [PsfHashtable]@{
    Answer = 42
    Conspiracy = 23
}
$mapping.EnablePassthru()

$mapping["Answer"] # 42
$mapping.Answer # 42
$mapping["Foo"] # Foo
$mapping.Foo # <nothing>

Note: One limitation with extending hashtables: The features on unknown keys only work, when using the index notation (e.g. $mapping["Foo"]), not the property notation (e.g. $mapping.Foo).

Default Value​

Rather than passing through the key, you can also provide a default value to return:

$mapping = [PsfHashtable]@{
    Answer = 42
    Conspiracy = 23
}
$mapping.SetDefaultValue(1)

$mapping["Answer"] # 42
$mapping.Answer # 42
$mapping["Foo"] # 1
$mapping.Foo # <nothing>

Note: One limitation with extending hashtables: The features on unknown keys only work, when using the index notation (e.g. $mapping["Foo"]), not the property notation (e.g. $mapping.Foo).

Dynamic Value​

A third alternative is to provide a custom scriptblock that gets executed on unknown keys:

$mapping = [PsfHashtable]@{
    Answer = 42
    Conspiracy = 23
}
$mapping.SetCalculator({ $_ * 2 })

$mapping["Answer"] # 42
$mapping.Answer # 42
$mapping["Foo"] # FooFoo
$mapping.Foo # <nothing>

Note: One limitation with extending hashtables: The features on unknown keys only work, when using the index notation (e.g. $mapping["Foo"]), not the property notation (e.g. $mapping.Foo).

More ways to get PsfHashtables​

ConvertTo-PSFHashtable

The command ConvertTo-PSFHashtable offers an -AsPsfHashtable parameter:

Get-Item . | ConvertTo-PSFHashtable -AsPsfHashtable

It does not configure any of the special behaviors/features described above, but you can configure tham as described.

New-PSFHashtable

The command New-PSFHashtable allows you to predefine a hashtable with all the settings, no need to call any methods:

New-PSFHashtable -DefaultValue 42
New-PSFHashtable -PassThru
New-PSFHashtable -Calculator { $_ * 2 }