| description | title | ms.date | ms.assetid |
|---|---|---|---|
Learn more about: Boxing (C++/CX) | Boxing (C++/CX) | 12/30/2016 | edfb12fa-2a9b-42f6-bdac-d4d76cb8274e |
Boxing is wrapping a value type variable such as Windows::Foundation::DateTime—or a fundamental scalar type such as int—in a ref class when the variable is passed to a method that takes Platform::Object^ as its input type.
Although you don't have to explicitly box a variable to pass it to a method parameter of type Platform::Object^, you do have to explicitly cast back to the original type when you retrieve values that have been previously boxed.
[!code-cppcx_boxing#01]
C# and Visual Basic support the concept of nullable value types. In C++/CX, you can use the Platform::IBox<T> type to expose public methods that support nullable value type parameters. The following example shows a C++/CX public method that returns null when a C# caller passes null for one of the arguments.
[!code-cppcx_boxing#02]
In a C# XAML client, you can consume it like this:
// C# client code BoxingDemo.Class1 obj = new BoxingDemo.Class1(); int? a = null; int? b = 5; var result = obj.Multiply(a, b); //result = null Type System (C++/CX)
Casting (C++/CX)
C++/CX Language Reference
Namespaces Reference
