6.語言特性 · Haxe 3 手冊

**抽象類型**（第2.8節）：一個抽象類型是一個編譯時構造，在運行時以一個不同的方式表示。這允許給存在的類型一個全新的意義。 > Abstract types (2.8): > An abstract type is a compile-time construct which is represented in a different way at runtime. This allows giving a whole new meaning to existing types. **外部類**（第6.2節）：外部類可以被用于以一個類型安全的方式描述目標語言特定的交互。 > Extern classes (6.2): > Externs can be used to describe target-speci?c interaction in a type-safe manner. **匿名結構**（第2.5節）：數據可以被簡單的組織為匿名結構，減少小型數據類的必要性。 > Anonymous structures (2.5): > Data can easily be grouped in anonymous structures, minimizing the necessity of small data classes. ~~~ var point = { x: 0, y: 10 }; point.x += 10; ~~~ **數組推導**（第6.6節）：使用 for 循環和一些邏輯快速創建和填充數組。 > Array Comprehension (6.6): > Create and populate arrays quickly using for loops and logic. ~~~ var evenNumbers = [ for (i in 0...100) if (i\%2==0) i ]; ~~~ **類，接口和繼承**（第2.3節）： Haxe允許用類組織代碼，使其成為一個面向對象語言。通常相關的功能如Jave等語言所支持的，包括繼承和接口。 > Classes, interfaces and inheritance (2.3): > Haxe allows structuring code in classes, making it an object-oriented language. Common related features known from languages such as Java are supported, including inheritance and interfaces. **條件編譯**（第6.1節）：條件編譯允許根據編譯參數編譯特定的代碼。這有助于抽象目標語言特定的差異，但是也可以用于其他的目的，如更詳細的調試。 > Conditional compilation (6.1): > Conditional Compilation allows compiling speci?c code depending on compilation parameters. This is instrumental for abstracting target-speci?c differences,but can also be used for other purposes, such as more detailed debugging. ~~~ \#if js js.Browser.alert("Hello"); \#elseif sys Sys.println("Hello"); \#end ~~~ **（廣義的）代數數據類型**（第2.4節）：結構可以通過代數數據類型（ADT）描述，如Haxe語言中的枚舉。除此之外，Haxe支持它們的廣義的變體如GADT。 > (Generalized) Algebraic Data Types (2.4): > Structure can be expressed through algebraic data types (ADT), which are known as enums in the Haxe Language. Furthermore, Haxe supports their generalized variant known as GADT. ~~~ enum Result { Success(data:Array<Int>); UserError(msg:String); SystemError(msg:String, position:PosInfos); } ~~~ **內聯調用**（第4.4.2節）：函數可以被設計為內聯，使它們的代碼直接插入調用的位置。通過手動的內聯不用使代碼重復這可以產生顯著的效能提升。 > Inlined calls (4.4.2): > Functions can be designated as being inline, allowing their code to be inserted at call-site. This can yield signi?cant performance bene?ts with out resorting to code duplication via manual inlining. **迭代器**（第6.7節）：迭代一組值，例如一個數組的元素，在Haxe中可以很容易的迭代。定制類可以快速的實現迭代器功能來允許迭代。 > Iterators (6.7): > Iterating over a set of values, e.g. the elements of an array, is very easy in Haxe courtesy of iterators. Custom classes can quickly implement iterator functionality to allow iteration. ~~~ for (i in [1, 2, 3]) { trace(i); } ~~~ **局部函數和閉包**（第5.11節）： Haxe中的函數不限于類字段，并可以被聲明為表達式，允許強大的閉包。 > Local functions and closures (5.11): > Functions in Haxe are not limited to class ?elds and can be declared in expressions as well, allowing powerful closures. ~~~ var buffer = ""; function append(s:String) { buffer += s; } append("foo"); append("bar"); trace(buffer); // foobar ~~~ **元數據**（第6.9節）：添加元數據到字段，類或者表達式。這可以和編譯器、宏，或者運行時的類溝通信息。 > Metadata (6.9): > Add metadata to ?elds, classes or expressions. This can communicate information to the compiler, macros, or runtime classes. ~~~ class MyClass { @range(1, 8) var value:Int; } trace(haxe.rtti.Meta.getFields(MyClass).value.range); // [1,8] ~~~ **靜態擴展**（第6.3節）：存在的類和其它類型可以被額外的功能來擴展，通過使用靜態擴展。 > Static Extensions (6.3): > Existing classes and other types can be augmented with additional functionality through using static extensions. ~~~ using StringTools; " Me & You ".trim().htmlEscape(); ~~~ **字符串插值**（第6.5節）：字符串通過一個單引號聲明，可以在當前的上下文訪問變量。 > String Interpolation (6.5): > Strings declared with a single quotes are able to access variables in the current context. ~~~ trace(’My name is $name and I work in ${job.industry}’); ~~~ **偏函數應用**（第6.8節）：任何函數可以應用為局部的，提供某些參數的值，然后保留其它的作為之后的字段。 > Partial function application (6.8): > Any function can be applied partially, providing the values of some arguments and leaving the rest to be ?lled in later. ~~~ var map = new haxe.ds.IntMap(); var setToTwelve = map.set.bind(_, 12); setToTwelve(1); setToTwelve(2); ~~~ **模式匹配**（第6.4節）：復雜的結構可以被根據模式來匹配，從一個枚舉或者一個結構中提取信息，并對特定的值組合定義特定的操作。 > Pattern Matching (6.4): > Complex structures can be matched against patterns, extracting information from an enum or a structure and de?ning speci?c operations for speci?c value combination. ~~~ var a = { foo: 12 }; switch (a) { case { foo: i }: trace(i); default: } ~~~ **屬性**（第4.2節）：變量類字段可以被涉及為屬性，通過定制的read和write訪問，可以更精細的訪問控制。 > Properties (4.2): > Variable class ?elds can be designed as properties with custom read and write access, allowing ?ne grained access control. ~~~ public var color(get,set); function get_color() { return element.style.backgroundColor; } function set_color(c:String) { trace(’Setting background of element to $c’); return element.style.backgroundColor = c; } ~~~ **訪問控制**（第6.10節）：訪問控制語言特性使用Haxe元數據語法來禁止或者允許訪問類或者字段。 > Access control (6.10): > The access control language feature uses the Haxe metadata syntax to force or allow access classes or ?elds. **類型參數、約束和變異**（第3.2節）：類型可以通過類型參數來參數化，使類型化的容器和其它復雜的數據結構可用。類型參數也可以被約束為某些類型并遵守變異規則。 > Type Parameters, Constraints and Variance (3.2): > Types can be parametrized with type parameters, allowing typed containers and other complex data structures. Type parameters can also be constrained to certain types and respect variance rules. ~~~ class Main<A> { static function main() { new Main<String>("foo"); new Main(12); // use type inference } function new(a:A) { } } ~~~