Enumerable.Cast(Of TResult) Method

July 28, 2014

Converts the elements of an IEnumerable to the specified type.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)

'Declaration
<ExtensionAttribute> _
Public Shared Function Cast(Of TResult) ( _
	source As IEnumerable _
) As IEnumerable(Of TResult)

Type Parameters

TResult

The type to convert the elements of source to.

Parameters

source
Type: System.Collections.IEnumerable
The IEnumerable that contains the elements to be converted.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TResult)
An IEnumerable(Of T) that contains each element of the source sequence converted to the specified type.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable. When you use instance method syntax to call this method, omit the first parameter.

ExceptionCondition
ArgumentNullException

source is Nothing.

InvalidCastException

An element in the sequence cannot be cast to type TResult.

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.

The Cast(Of TResult)(IEnumerable) method enables the standard query operators to be invoked on non-generic collections by supplying the necessary type information. For example, System.Collections.ArrayList does not implement IEnumerable(Of T), but by calling Cast(Of TResult)(IEnumerable) on the System.Collections.ArrayList object, the standard query operators can then be used to query the sequence.

If an element cannot be cast to type TResult, this method will throw an exception. To obtain only those elements that can be cast to type TResult, use the OfType(Of TResult) method instead of Cast(Of TResult)(IEnumerable).

In a query expression, an explicitly typed iteration variable translates to an invocation of Cast(Of TResult)(IEnumerable). This example shows the syntax for an explicitly typed range variable.

From i As Integer In objects

The following code example demonstrates how to use Cast(Of TResult)(IEnumerable) to enable the use of the standard query operators on an System.Collections.ArrayList.


      ' Create an ArrayList and add items to it.
      Dim fruits As New List(Of String)()
      fruits.Add("apple")
      fruits.Add("mango")

      ' Call Cast(Of String) to cast the ArrayList elements to strings.
      ' Then call Select() to project the strings as the query result.
      Dim query As IEnumerable(Of String) = _
          fruits.Cast(Of String)().Select(Function(fruit) fruit)

      Dim output As New System.Text.StringBuilder
      For Each fruit As String In query
         output.AppendLine(fruit)
      Next

      ' Display the output.
      outputBlock.Text &= output.ToString() & vbCrLf

      ' This code produces the following output:
      '
      ' apple
      ' mango



Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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