about_Calling_Generic_Methods

Generics let you tailor a method, class, structure, or interface to the precise data type it acts upon. For example, instead of using the System.Collections.Hashtable class, which allows keys and values to be of any type, you can use the System.Collections.Generic.Dictionary%602 generic class and specify the types allowed for the key and value properties. Generics provide increased code reusability and type safety.

For some generic methods, PowerShell is able to figure out generic arguments for a method by inferring from the provided arguments. However, method resolution can be complicated when a method has both generic and non-generic overloads, or when the generic method takes no formal parameter. PowerShell can fail to resolve the correct method without the explicit generic method arguments.

For example, [array]::Empty<T>(). The .NET Array class has a static, generic method Empty<T>() that takes no formal parameters.

Prior to PowerShell 7.3, to ensure proper method resolution you had to use complicated workarounds using .NET reflection. For an example, see Lee Holmes' blog post Invoking generic methods on non-generic classes in PowerShell.

Beginning with PowerShell 7.3, you can specify the types for a generic method.

Syntax

A generic method is a method with two parameter lists: a list of generic types and a list of method arguments.

The following examples show the new PowerShell syntax for accessing a generic method:

# static generic methods
[type_name]::MethodName[generic_type_arguments](method_arguments)

# instance generic methods
$object.MethodName[generic_type_arguments](method_arguments)

The generic_type_arguments can be a single type or comma-separated list of types, like [string, int], including other generic types like $obj.MethodName[string, System.Collections.Generic.Dictionary[string, int]]()

The method_arguments can be zero or more items.

For more information, see Generics in .NET.

Example

In this example, we create a list of integers then use the System.Linq.Enumerable class to enumerate the values and transform them to a new value.

The variable $list is a generic List<T> object that can only contain integers. List<T> is a generic class that allows you to specify the type of its members when you create it. [System.Linq.Enumerable]::Select<T1,T2>(T1,T2) is a generic method that require two generic type parameters and two formal value parameters.

[System.Collections.Generic.List[int]]$list = @( 1, 2, 3, 4, 5 )
$result = [System.Linq.Enumerable]::Select[int, float](
    $list,
    [Func[int, float]]{
        param($Item)
        [Math]::Pow($Item, 3)
    }
)
$result

The output shows each value raised to the power of 3.

1
8
27
64
125