System.Collections.Hashtable (class)

Derivation and interfaces

System.Collections.Hashtable derives directly from System.Object and implements System.IClonable and IDictionary.

There is no Hashtable<TKey, TValue>

Unlike many other classes in the System.Collections namespaces, there is no counterpart with the name System.Collections.Generic.Hashtable<TKey, TValue>. However, there is a System.Collections.Generic.Dictionary<TKey, TValue> class.

In fact, Microsoft recommends to use the Dictionary<TKey, TValue> class.

Using hashtables in PowerShell

Create a hashtable

In PowerShell, a hash table can be created like so:

PS: C:\> $ht = @{
  key_1 = 'foo'
  key_2 = 'bar'
  key_3 = 'baz'
}

PS: C:\> $ht.GetType().FullName
System.Collections.Hashtable

Adding a value to a hash table

PS: C:\> $ht.key_4 = 'added'

Iterating over elements

The hashtable's property keys (whose type is System.Collections.Hashtable+KeyCollection which implements System.Collections.ICollection and System.Collections.IEnumerable) provides the names of the keys in the hashtable. This allows to iterate over the key/value pairs:

$ht.keys | foreach-object { "$_ -> $($ht[$_])" }

GetEnumerator() returns a an enumerator that provides System.Collections.DictionaryEntry objects with the two properties Key (apparently aliased to Name in PowerShell) and Value:

$ht.GetEnumerator() | foreach-object { "$($_.key) -> $($_.value)" }

Using hash tables for splatting

Hash tables can be used for function parameter splatting.