Windows Runtime

"WinRT" redirects here.

Not to be confused with Windows RT.

Windows Runtime

Developer(s)	Microsoft
Operating system	Windows 8, Windows RT, Windows Phone 8
Type	Software framework
License	Proprietary; Parts under other licenses.
Website	www.microsoft.com

Windows Runtime, or WinRT, is a platform-homogeneous application architecture on the Windows 8 operating system. WinRT supports development in C++/CX (Component Extensions, a language based on C++) and the managed languages C# and VB.NET, as well as JavaScript and TypeScript. WinRT applications natively support both the x86 and ARM architectures, and also run inside a sandboxed environment to allow for greater security and stability.

WinRT is essentially a COM-based API, although relying on an enhanced COM. Due to its COM-like basis, WinRT allows interfacing from multiple languages, just as COM does, but it's essentially an unmanaged, native API. The API definitions are, however, stored in ".winmd" files, which are encoded in ECMA 335 metadata format, the same format that .NET uses with a few modifications. This common metadata format allows for significantly less overhead when invoking WinRT from .NET applications compared to P/Invoke, and much simpler syntax. The new C++/CX (Component Extensions) language, which borrows some C++/CLI syntax, allows the authoring and consumption of WinRT components with less glue visible to the programmer compared to classic COM programming in C++, and at the same time imposes fewer restrictions compared to C++/CLI on the mixing of types. Regular C++ (with COM-specific discipline) can also be used to program with WinRT components, with the help of the new Windows Runtime C++ Template Library (WRL), which is similar in purpose to what Active Template Library provides for COM. The MSDN Library, however, recommends using C++/CX instead of WRL.

Applications developed using WinRT for Windows 8 and RT are known as Windows Store apps. During the development of Windows 8, they were referred to as Metro-style apps; a term tying them in with a design language of the same name used heavily throughout the operating system. However, the term began to be phased out in August 2012—while reports stated that Microsoft warned developers to stop using the term due to trademark issues with a company of a similar name, a spokesperson claimed that "Metro" was only a codename and that an official name was to be unveiled. The terms Windows 8 style, Modern UI style were also used interchangeably by Microsoft employees and documents to refer to the new app platform prior to the launch of Windows 8.

Windows Phone 8 uses a version of the Windows Runtime known as the Windows Phone Runtime. It enables app development in C#, VB.NET and development of Windows Runtime components in C++/CX.

Technology

WinRT components are designed with an eye to interoperability between multiple languages and APIs, including native, managed and scripting. For example the Component Extensions of C++/CX are recommended to be used only at the API-boundary, not for other purposes.

WinRT applications will run within a sandbox. Examination of the runtime libraries reveals that they are built upon Win32 API. This is the same approach used by .NET.

Services

Metadata

See also: Metadata (CLI)

The metadata describes the code written for the WinRT platform. It defines a programming model that makes it possible to write object-oriented code that can be shared across programming languages. It also enables services like reflection.

Herb Sutter, C++ expert at Microsoft, explained during his session on C++ at the BUILD-conference that the WinRT metadata is CLI metadata. Native code (processor specific) cannot contain metadata and it is then stored in separate WINMD-files that can be reflected just like ordinary CLI assemblies.

Because it is CLI metadata the programmer can then use code written in native WinRT-languages from managed CLI languages.

Type system

WinRT has a rich object-oriented class-based type system that is built on the metadata. It supports constructs with corresponding constructs that are found in the .NET framework: classes, methods, properties, delegates and events.

One of the major additions to WinRT relative to COM is the cross-ABI, .NET-style generics. In C++/CX these are declared using the generic keyword with a syntax very similar to that of the template keyword. WinRT classes (ref classes) can also be genericized using C++ templates but only template instantiations can be exported to .winmd metadata (with some name mangling), unlike WinRT generics which preserve their genericity in the metadata. WinRT also provides a library of generic containers that parallel those from the C++ standard library, as well as some back-and-forth conversion functions. The consumption of WinRT collections in .NET languages (e.g. C# and VB) as well as in JavaScript is more transparent than in the case of C++, with automated mappings into their natural equivalents taking place behind the scenes. When authoring a WinRT component in a managed language, some extra, COM-style rules need to be followed, e.g. .NET framework collection types cannot be declared as return types, but only the WinRT interfaces that they implement can be used at the component boundary.

WinRT components

Classes that are compiled to target the WinRT are called WinRT components. They are classes that can be written in any supported language and for any supported platform. The key is the metadata. This metadata makes it possible to interface with the component from any other WinRT language. The runtime requires WinRT components that are built with .NET Framework to use the defined interface types or .NET type interfaces, which automatically map to the first named. Inheritance is as yet not supported in managed WinRT components, except for XAML classes.

Programming interfaces

Programs and libraries targeted for the WinRT runtime can be created and consumed from a number of platforms and programming languages. Notably C/C++ (either with language extensions offering first-class support for WinRT concepts, or with a lower-level template library allowing to write code in standard C++), .NET (C# and VB.NET) and JavaScript. This is made possible by the metadata.

In WinRT terminology, a language binding is referred to as a language projection.

C++ (WRL, Component Extensions)

See also: C++/CX

Native C++ is a "first-class citizen" of the WinRT-platform. To use WinRT from C++ two supported options are available: WRL—an ATL-style template library—and C++/CX (C++ with Component Extensions) which resembles C++/CLI. Because of the internal consumption requirements at Microsoft, WRL is exception-free, meaning its return-value discipline is HRESULT-based just like that of COM. C++/CX on the other hand wraps-up calls to WinRT with code that does error checking and throws exceptions as appropriate.

C++/CX has a number of extensions that enable integration with the platform and its type system. The syntax resembles the one of C++/CLI although it produces native code and metadata that integrates with the runtime. For example WinRT objects may be allocated with ref new, which is the counterpart of gcnew from C++/CLI. The hat operator (^) retains its meaning, however in the case where both the caller and callee are written in C++ and living in the same process, a hat reference is simply a pointer to a vptr to a vtable.

An addition to C++/CX relative to traditional C++ COM programming are partial classes, again inspired from .NET. These allow for instance XAML code to be translated into C++ code by tools and then combined with human-written code to produce the complete class while allowing clean separation of the machine-generated and human-edited parts of a class implementation into different files.

WinRT is a native platform and supports any native C++ code. A C++ developer can reuse existing native C/C++ libraries with the only need to use the language extensions when writing code that is interfacing with the runtime.

Delphi

Despite claims of interoperability between multiple languages a pratical attempt to implement independent binding to WinRT for a native language is currently doomed to fail . Allen Bauer wrote:

We are very keen on supporting WinRT with native Delphi & C++ code. Right now, the issues surrounding the WinRT space center around the fact that many OS-supplied APIs which are required by anyone implementing their own language RTL are actually off-limits unless you're the VC++ RTL DLL. You know, little things like RtlUnwind for exception processing and VirtualAlloc (et. al.) for memory management... Any calls to those APIs from your application will automatically disqualify your application from being an "official" WinRT application capable of delivering through the MS app store.

Right now the VC++ RTL DLL is given special dispensation since that is the library that makes the calls to those forbidden APIs and not directly from the user's app. We're currently rattling some cages at MS to find out how or if they're going to allow third-party tools to target WinRT. Until we can get past that, targeting WinRT isn't actually possible from a deliverable product sense. We are able to build WinRT applications with Delphi that work with a developer certificate, however they all fail the application qualification checks because of the aforementioned (an other) APIs.

Due to this unsolved issue recent Delphi compilers feature Metropolis instead of Metro. In order to display a live tile a Metropolis application uses additional proxy application. A proxy application is written in a language permitted by Microsoft censorship and compiled with a compiler permitted by Microsoft censorship, so it has no problem to display a live tile, and the main application is written in a language developers should know better than to do what Microsoft permits.

.NET

See also: .NET Framework

The .NET Framework and the Common Language Runtime (CLR) are integrated into the WinRT as a subplatform. It also has influenced and set the standards for the ecosystem through the metadata format and libraries. The CLR provides services like JIT-compilation code and garbage collection. WinRT applications using .NET languages use the new Windows Runtime XAML Framework, and are primarily written in C#, VB.NET and Oxygene (and for the first time for XAML with native code using C++/CX). Although not yet officially supported, programs can also be written in other .NET languages.

Limitations
Classes defined in WinRT components that are built in managed .NET languages must be declared as sealed, so they cannot be derived from. However, non-sealed WinRT classes defined elsewhere can be inherited from in .NET, their virtual methods overridden, and so on (but the inherited managed class must still be sealed).

Members that interface with another language must have a signature with WinRT types or a managed type that is convertible to these.

JavaScript

See also: JavaScript and Rich Internet Application

WinRT applications can also be coded using HTML with JavaScript in code-behind, which are run using the Trident rendering engine and Chakra JavaScript engine, both of which are also used by Internet Explorer. When coding a WinRT app in JavaScript, its features are adapted to follow JavaScript naming conventions, and namespaces are also mapped to JavaScript objects.

API

WinRT comes with an Application Programming Interface (API) in the form of a class library that exposes the features of Windows 8 for the developer, like its immersive interface API. It is accessible and consumable from any supported language.

Windows classes

The Windows classes are native C/C++ libraries (unmanaged) that are exposed by the WinRT. They provide access to all functionality from the XAML parser to the camera function.

Naming conventions

The naming conventions for the components (classes and other members) in the API are heavily influenced by the .NET naming conventions which uses camel case (specifically PascalCase). Microsoft recommends users to follow these rules in case where no others are given.

These conventions are projected differently in some languages, like JavaScript, which converts it to its conventions and the other way around. This is to give a native and consistent experience regardless of the programming language.

Restrictions and rules

Since Windows Runtime is projected to various languages, some restrictions on fundamental data types exist in order to host all of these languages. Programmers have to be careful with the behavior of those types when used with public access (for method parameters, method return values, properties, etc.).

• Basic Types
  • In .NET languages and C++, there is a rich set of data types representing various numerals.
  • In JavaScript, a Number can only represent up to 53 bits of precision.
  • In WinRT, the only lacking numeral data type is 8-bit signed integer when compared to .NET and C++. JavaScript developers have to pay attention when dealing with big numbers while coding against WinRT.

• Strings
  • The strings in .NET and JavaScript are immutable, whereas they are mutable in C++.
  • A null pointer passed as a string to WinRT by C++ will be converted to an empty string
  • In .Net null being passed as a string to WinRT will be converted to an empty string
  • In Javascript null being passed as a string to WinRT will be converted to a string with the word "null". This is due to Javascript's null keyword being represented as a null object
    • Similar results happen when passing undefined to WinRT from Javascript

• Structs
  • In .NET and C++, structs are value types, and such a struct can contain any type in it.
  • JavaScript does not directly support structs.
  • In WinRT, usage of structs is only allowed for containment of types that has value semantics, including numerals, strings, and other structs. No pointers or interface references are allowed.

• References
  • In .NET, objects are passed by reference, whereas numerals and structs are passed by value.
  • In C++, all types can be passed by reference or by value.
  • In WinRT, interfaces are passed by reference; all other types are passed by value.

• Arrays
  • In .NET, C++, and JavaScript arrays are reference types.
  • In WinRT, arrays are value types.

• Events
  • In .NET and C++, clients subscribe to events using += operator.
  • In JavaScript, addEventListener function or setting on<EventName> property is used to subscribe to events.
  • In WinRT, all languages are allowed to use their own way of subscribing to events.

• Collections
  • Various .NET collections map directly to WinRT collections.
  • WinRT Vector type resembles arrays and the array syntax is used to consume them.
  • WinRT Map type is a key/value pair collection, and is projected as Dictionary in .NET languages.

• Method Overloading
  • All WinRT languages feature overloading on parameters (.NET, C++, JavaScript)
  • .NET and C++ also feature overloading on type.
  • In WinRT, only parameter number is used for overloading.

• Asynchrony
  • All WinRT methods are designed such that any method taking longer than 50 milliseconds is an async method.
  • There is an established naming pattern to distinguish asynchronous methods: <Verb>[<Noun>]Async. Through the entire runtime library, all methods that have chance to take longer than 50 ms are only implemented as asynchronous methods.

Windows Phone Runtime

Windows Phone 8 has limited support for development and consuming of Windows Runtime components through Windows Phone Runtime. Many of the Windows Runtime APIs in Windows 8 that handle core operating-system functionality have been ported to Windows Phone 8. Support for development of native games using C++/CX and DirectX has been added by request from the game development industry.

The Windows Phone XAML Framework is however still based on the same Silverlight framework as in Windows Phone 7 for backwards compatibility. XAML development is therefore not currently possible in C++/CX. Neither development using HTML5 and WinJS is supported on Windows Phone 8 at the moment.

See also

• Windows Runtime XAML Framework

External links

• WinRT documentation (preview) at Windows Dev Center