Lessons learned designing the Windows Runtime

1. PLAT-876T Lessons learned designing the Windows Runtime Brent Rector Senior Program Manager Microsoft Corporation

2. Agenda • Design considerations building a multi-language OS runtime • How these decisions affect coding in your preferred language • Apply this knowledge in your Metro style apps

3. Agenda Please • Don’t make me write this again! RT

4. Windows Runtime APIs • Available to all programming languages • Requires a language neutral type system

5. Casing of APIs in multiple languages • Many languages use PascalCasing for names of types, methods, properties, and events • JavaScript has well established naming conventions • “Types” are PascalCased • Methods and Properties are camelCased • Events are all lowercase • Windows Runtime uses PascalCasing for types and members • JavaScript maps methods, properties and event names to its conventions • Causes oddities occasionally – UIElement -> uielement

6. Windows Runtime types

7. Numeric types • Behave differently in .NET/C++ compared to JavaScript • C++/.NET - Signed, Unsigned; 8, 16, 32, 64 bit int; 32, 64 bit float • JavaScript – double-precision 64-bit binary format IEEE 754 value • Windows Runtime – Same as C++/.NET without signed 8-bit integer • But… • Operating system uses 64-bit integers in some places • file sizes, position, etc. • JavaScript number can only represent 53 bits of precision

8. Numeric types • ECMAScript (ECMA-262) Standard • Requires numbers treated as IEEE-754 64-bit floating point values • JavaScript applications using the Chakra runtime cannot accurately determine the values of some 64-bit integers • But such values can be received from and passed back to WinRT APIs • Many (most) values will work fine • Use caution with 64 bit values whose absolute value is greater than 2^53 (9,007,199,254,740,992)

9. publicrefclassMyClasssealed { • __int64 _largeNumber; • MyClass() { _largeNumber= 9007199254740992 + 7; } • property__int64LargeNumber { • __int64 get() { return _largeNumber; } • voidset(__int64value) { _largeNumber= value; } • } • boolCompareInt64(__int64 a, __int64 b) { return a == b; } • };

10. var b = newMyLibrary.MyClass(); • var val1 = b.largeNumber; • var val2 = b.largeNumber; • varisEqual = b.compareInt64(val1, val2); // true • val1 = val1 + 0; • isEqual = b.compareInt64(val1, val2); // false

11. Windows Runtime types

12. Strings • Immutable or mutable? • Immutable – JavaScript, .NET; Mutable – C++ • Null • JavaScript: null is an object, string is a type • C++: std::string has no 'null' semantics • .NET System.String: reference type has a 'null' distinguished value • Windows Runtime: string's immutable, no null representation

13. publicrefclassMyClasssealed { • Platform::String^ _myString; • MyClass() {_myString = nullptr; } • propertyPlatform::String^ MyString { • Platform::String^ get() { return _myString; } • void set(Platform::String^ value) { • _myString = value; } • } • };

14. vars = b.myString; • // What is the value of ‘s’? • b.myString= null; • vars = b.myString; • // What is the value of ‘s’? • b.myString = ""; • vars = b.myString; • // What is the value of ‘s’

15. Windows Runtime types

16. Structures • Handled differently by languages • C++/CLR: Structures are value types, can contain all types • JavaScript: Has no structure construct but structures can be simulated • Windows Runtime supports structures, with restrictions on content • Can only contain numbers, strings or structures • Windows Runtime structures cannot contain pointers • Windows Runtime structures are value types • As a result… • Structure valued property behavior differs in languages

17. using namespace Windows::Foundation; • publicrefclassMyClasssealed { • Rect _myBounds; • propertyRectMyBounds{ • Rectget() { return _myBounds; } • void set(Rect value) { _myBounds= value; } • } • };

18. b.myBounds = {x: 100, y: 200, width: 300, height: 400 }; • b.myBounds.width= 42; • // What is the value of ‘width’? • b.myBounds = {x:b.myBounds.x, • y:b.myBounds.y, • width:42, • height:b.myBounds.height}; • var bounds = b.myBounds; • bounds.width = 42; • // What is the value of ‘b.myBounds.width’?

19. Windows Runtime types

20. References & pointers • Target languages handle pointers and references differently • C++: All types can be passed by value or by reference • .NET: Objects are passed by reference, value types by value • JavaScript: Objects passed by reference, numbers passed by value • Windows Runtime: Objects (Interfaces) passed by reference, all other types passed by value • As a result… • Method parameters are [in] or [out], never [in, out]

21. Windows Runtime types

22. Arrays • Reference or value types? • JavaScript, .NET, C++: Reference types • Windows Runtime • Arrays are value types so marshal by value • ONLY WHEN they are marshaled!

23. publicrefclassMyClasssealed { • voidArrayMethod (array<int>^ arr) { arr[0] = 42; } • void ArrayMethod2 (array<double>^ arr) { arr[0] = 42.0; } • };

24. vararr = { 1, 2, 3, 4, }; • b.ArrayMethod (arr); • // What is the value of arr[0]? • b.ArrayMethod2(arr); • // What is the value of arr[0]?

25. Windows Runtime types

26. Events • Event syntax differs across languages • C++/CLR – Clients add events with += operator • JavaScript – Clients add events with either the addEventListener function or by setting the “on<eventname>” property on the object. • Be aware… • JavaScript event name casing is all lowercase • Assigning to the property implies one listener while addEventListener allows multiple listeners • Misspelling the event name in either case silently fails

27. public ref class SignaledEventArgs sealed { • public: SignaledEventArgs() { }; • }; • public delegate void SignaledEventHandler( • Platform::Object^ sender, • SignaledEventArgsargs); • publicrefclassMyClasssealed { • event SignaledEventHandler^ Signaled; • };

28. var b = newMyLibrary.MyClass(); • b.addEventListener ("Signaled", function () { … }); • // What just happened? • b.addEventListener("signaled", function () { … }); • b.onSignaled = function () { … }; • // What just happened? • b.onsignaled= function () { … };

29. Events vs. delegates • Windows Runtime prefers events over delegate-typed properties • Both are (potentially) multi-cast • JavaScript nicely maps events to JavaScript event conventions • addEventListener (“eventname”, func) • oneventname property • Delegate properties are just that: properties • No addEvetListener form • Normal camelCasing of property name occurs: eventName

30. Windows Runtime types

31. Collections • Windows Runtime collections are relatively straightforward • Vectors – similar to array, projected with array syntax • Maps – key/value pairs, projected as dictionary to CLR apps • Surprise… • Because collection value accesses require a method call, they can be unexpected performance bottlenecks • Can use the GetMany method for bulk retrieval

32. Method overloading • Two criteria used when handling overloads • Overload on number of params (arity) • JavaScript, .NET, C++ all distinguish methods by arity • Overload on parameter type • .NET, C++ all distinguish methods by type of parameters • JavaScript has a limited notion of type • Windows Runtime methods • Overload on arity but not on type

33. publicrefclassMyClasssealed { • Platform::String^ AnOverload (Platform::String^ a) { • return a; • } • Platform::String^ AnOverload (Platform::String^ a, • Platform::String^ b) { • return a + b • } • };

34. varstr = b.AnOverload ("Hello"); // What just happened? • varstr = b.anOverload("Hello"); // What just happened? • varstr = b.anOverload ("Hello", " audience"); • // What just happened? • varstr = b.anOverload ("Hello", " audience", " at BUILD"); • // What just happened?

35. Asynchronous APIs • Platform design goal that APIs cannot block the UI thread • Guidance: Anything taking > 50 ms should be asynchronous • Resulted in prevalent use of Async Pattern in platform • Established a naming pattern: <verb>[<noun>]Async • GetThumbnailAsync • Return value mapped to a promise for a future result • In .NET – await obj.GetThumbnailAsync() • In JavaScript – obj.GetThumbNailAsync().then (func);

36. Further reading and documentation • C++ language extension summary • The Windows Runtime • Windows Runtime Design

37. thank you Feedback and questions http://forums.dev.windows.com Session feedbackhttp://bldw.in/SessionFeedback

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