Enumerable.Cast<TResult> Method
Casts the elements of an IEnumerable to the specified type.
Assembly: System.Core (in System.Core.dll)
Type Parameters
- TResult
The type to cast the elements of source to.
Parameters
- source
- Type: System.Collections.IEnumerable
The IEnumerable that contains the elements to be cast to type TResult.
Return Value
Type: System.Collections.Generic.IEnumerable<TResult>An IEnumerable<T> that contains each element of the source sequence cast 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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).| Exception | Condition |
|---|---|
| ArgumentNullException |
source is null. |
| 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<TResult>(IEnumerable) method enables the standard query operators to be invoked on non-generic collections by supplying the necessary type information. For example, ArrayList does not implement IEnumerable<T>, but by calling Cast<TResult>(IEnumerable) on the 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<TResult> method instead of Cast<TResult>(IEnumerable).
In a query expression, an explicitly typed iteration variable translates to an invocation of Cast<TResult>(IEnumerable). This example shows the syntax for an explicitly typed range variable.
The following code example demonstrates how to use Cast<TResult>(IEnumerable) to enable the use of the standard query operators on an ArrayList.
System.Collections.ArrayList fruits = new System.Collections.ArrayList();
fruits.Add("apple");
fruits.Add("mango");
IEnumerable<string> query =
fruits.Cast<string>().Select(fruit => fruit);
foreach (string fruit in query)
{
Console.WriteLine(fruit);
}
// This code produces the following output:
//
// apple
// mango
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
This is a link from stackoverflow.com and I think it's useful to know when trying to cast a collection with a custom explicit casting...and why it does not work.
http://stackoverflow.com/questions/2819473/linq-cast-extension-method-fails-but-typeobject-works
- 9/26/2011
- D. Casals
- 11/13/2011
- Thomas Lee
Consider the following code:
var intSequence = Enumerable.Range(1, 10);An InvalidCastException will be thrown on the second line. To see why, consider what happens when you iterate a non-generic IEnumerable. You must do so by accessing each element as an object. That means that an IEnumerable of value types will return boxed values. Trying to cast the box to a type that differs from the type that is actually boxed is illegal, and will throw the IllegalCastException.
var longSequence = intSequence.Cast<long>();
