流式接口

流式接口（fluent interface）是软件工程中面向对象API的一种实现方式，以提供更为可读的源代码。最早由Eric Evans（英语：Eric Evans (technologist)）与Martin Fowler于2005年提出。 通常采取方法瀑布调用 (具体说是方法链式调用)来转发一系列对象方法调用的上下文 。这个上下文（context）通常是指： 通过被调方法的返回值定义 自引用，新的上下文等于老的上下文。 返回一个空的上下文来终止。 C++的iostream流式调用就是一个典型的例子。Smalltalk在1970年代就实现了方法瀑布调用。 用于数据库查询的jQuery，例如https://github.com/Medium/dynamite （页面存档备份，存于互联网档案馆） : // getting an item from a table client.getItem('user-table') .setHashKey('userId', 'userA') .setRangeKey('column', '@') .execute() .then(function(data) { // data.result: the resulting object }) JavaScript使用原型继承与`this`. // example from http://schier.co/post/method-chaining-in-javascript // define the class var Kitten = function() { this.name = 'Garfield'; this.color = 'brown'; this.gender = 'male'; }; Kitten.prototype.setName = function(name) { this.name = name; return this; }; Kitten.prototype.setColor = function(color) { this.color = color; return this; }; Kitten.prototype.setGender = function(gender) { this.gender = gender; return this; }; Kitten.prototype.save = function() { console.log( 'saving ' + this.name + ', the ' + this.color + ' ' + this.gender + ' kitten...' ); // save to database here... return this; }; // use it new Kitten() .setName('Bob') .setColor('black') .setGender('male') .save(); jOOQ库模拟了SQL Author author = AUTHOR.as("author"); create.selectFrom(author) .where(exists(selectOne() .from(BOOK) .where(BOOK.STATUS.eq(BOOK_STATUS.SOLD_OUT)) .and(BOOK.AUTHOR_ID.eq(author.ID)))); C#在LINQ中大量使用 standard query operators与扩展方法。 var translations = new Dictionary<string, string> { {"cat", "chat"}, {"dog", "chien"}, {"fish", "poisson"}, {"bird", "oiseau"} }; // Find translations for English words containing the letter "a", // sorted by length and displayed in uppercase IEnumerable<string> query = translations .Where (t => t.Key.Contains("a")) .OrderBy (t => t.Value.Length) .Select (t => t.Value.ToUpper()); // The same query constructed progressively: var filtered = translations.Where (t => t.Key.Contains("a")); var sorted = filtered.OrderBy (t => t.Value.Length); var finalQuery = sorted.Select (t => t.Value.ToUpper()); 流式接口可用于一系列方法，他们运行在同一对象上。 // Defines the data context class Context { public string FirstName { get; set; } public string LastName { get; set; } public string Sex { get; set; } public string Address { get; set; } } class Customer { private Context _context = new Context(); // Initializes the context // set the value for properties public Customer FirstName(string firstName) { _context.FirstName = firstName; return this; } public Customer LastName(string lastName) { _context.LastName = lastName; return this; } public Customer Sex(string sex) { _context.Sex = sex; return this; } public Customer Address(string address) { _context.Address = address; return this; } // Prints the data to console public void Print() { Console.WriteLine("First name: {0} \nLast name: {1} \nSex: {2} \nAddress: {3}", _context.FirstName, _context.LastName, _context.Sex, _context.Address); } } class Program { static void Main(string[] args) { // Object creation Customer c1 = new Customer(); // Using the method chaining to assign & print data with a single line c1.FirstName("vinod").LastName("srivastav").Sex("male").Address("bangalore").Print(); } } 下述代码对比了传统的风格与流式接口的实现风格： // Basic definition class GlutApp { private: int w_, h_, x_, y_, argc_, display_mode_; char **argv_; char *title_; public: GlutApp(int argc, char** argv) { argc_ = argc; argv_ = argv; } void setDisplayMode(int mode) { display_mode_ = mode; } int getDisplayMode() { return display_mode_; } void setWindowSize(int w, int h) { w_ = w; h_ = h; } void setWindowPosition(int x, int y) { x_ = x; y_ = y; } void setTitle(const char *title) { title_ = title; } void create(){;} }; // Basic usage int main(int argc, char **argv) { GlutApp app(argc, argv); app.setDisplayMode(GLUT_DOUBLE|GLUT_RGBA|GLUT_ALPHA|GLUT_DEPTH); // Set framebuffer params app.setWindowSize(500, 500); // Set window params app.setWindowPosition(200, 200); app.setTitle("My OpenGL/GLUT App"); app.create(); } // Fluent wrapper class FluentGlutApp : private GlutApp { public: FluentGlutApp(int argc, char **argv) : GlutApp(argc, argv) {} // Inherit parent constructor FluentGlutApp &withDoubleBuffer() { setDisplayMode(getDisplayMode() | GLUT_DOUBLE); return *this; } FluentGlutApp &withRGBA() { setDisplayMode(getDisplayMode() | GLUT_RGBA); return *this; } FluentGlutApp &withAlpha() { setDisplayMode(getDisplayMode() | GLUT_ALPHA); return *this; } FluentGlutApp &withDepth() { setDisplayMode(getDisplayMode() | GLUT_DEPTH); return *this; } FluentGlutApp &across(int w, int h) { setWindowSize(w, h); return *this; } FluentGlutApp &at(int x, int y) { setWindowPosition(x, y); return *this; } FluentGlutApp &named(const char *title) { setTitle(title); return *this; } // It doesn't make sense to chain after create(), so don't return *this void create() { GlutApp::create(); } }; // Fluent usage int main(int argc, char **argv) { FluentGlutApp(argc, argv) .withDoubleBuffer().withRGBA().withAlpha().withDepth() .at(200, 200).across(500, 500) .named("My OpenGL/GLUT App") .create(); } Ruby语言允许修改核心类，这使得流式接口成为原生易于实现。 # Add methods to String class class String def prefix(raw) "#{raw} #{self}" end def suffix(raw) "#{self} #{raw}" end def indent(raw) raw = " " * raw if raw.kind_of? Fixnum prefix(raw) end end # Fluent interface message = "there" puts message.prefix("hello") .suffix("world") .indent(8) Scala supports a fluent syntax for both method calls and class mixins, using traits and the with keyword. For example: class Color { def rgb(): Tuple3[Decimal] } object Black extends Color { override def rgb(): Tuple3[Decimal] = ("0", "0", "0"); } trait GUIWindow { // Rendering methods that return this for fluent drawing def set_pen_color(color: Color): this.type def move_to(pos: Position): this.type def line_to(pos: Position, end_pos: Position): this.type def render(): this.type = this // Don't draw anything, just return this, for child implementations to use fluently def top_left(): Position def bottom_left(): Position def top_right(): Position def bottom_right(): Position } trait WindowBorder extends GUIWindow { def render(): GUIWindow = { super.render() .move_to(top_left()) .set_pen_color(Black) .line_to(top_right()) .line_to(bottom_right()) .line_to(bottom_left()) .line_to(top_left()) } } class SwingWindow extends GUIWindow { ... } val appWin = new SwingWindow() with WindowBorder appWin.render() In Perl 6, there are many approaches, but one of the simplest is to declare attributes as read/write and use the given keyword. The type annotations are optional, but the native gradual typing makes it much safer to write directly to public attributes. class Employee { subset Salary of Real where * > 0; subset NonEmptyString of Str where * ~~ /\S/; # at least one non-space character has NonEmptyString $.name is rw; has NonEmptyString $.surname is rw; has Salary $.salary is rw; method gist { return qq:to[END]; Name: $.name Surname: $.surname Salary: $.salary END } } my $employee = Employee.new(); given $employee { .name = 'Sally'; .surname = 'Ride'; .salary = 200; } say $employee; # Output: # Name: Sally # Surname: Ride # Salary: 200 在PHP中，可以使用表示实例的特殊变量$this返回当前对象。因此返回$this将使方法返回实例。下面的示例定义了一个Employee类和三个方法来设置它的名称、姓和薪水。每个Employee类的实例允许调用这些方法。 <?php class Employee { public $name; public $surName; public $salary; public function setName($name) { $this->name = $name; return $this; } public function setSurname($surname) { $this->surName = $surname; return $this; } public function setSalary($salary) { $this->salary = $salary; return $this; } public function __toString() { $employeeInfo = 'Name: ' . $this->name . PHP_EOL; $employeeInfo .= 'Surname: ' . $this->surName . PHP_EOL; $employeeInfo .= 'Salary: ' . $this->salary . PHP_EOL; return $employeeInfo; } } # Create a new instance of the Employee class, Tom Smith, with a salary of 100: $employee = (new Employee()) ->setName('Tom') ->setSurname('Smith') ->setSalary('100'); # Display the value of the Employee instance: echo $employee; # Display: # Name: Tom # Surname: Smith # Salary: 100 Python通过在实例方法中返回`self`： class Poem(object): def __init__(self, content): self.content = content def indent(self, spaces): self.content = " " * spaces + self.content return self def suffix(self, content): self.content = self.content + " - " + content return self >>> Poem("Road Not Travelled").indent(4).suffix("Robert Frost").content ' Road Not Travelled - Robert Frost' bliki: FluentInterface. [2016-07-02]. （原始内容存档于2021-03-08）.  Martin Fowler's original bliki entry coining the term （页面存档备份，存于互联网档案馆） A Delphi example of writing XML with a fluent interface （页面存档备份，存于互联网档案馆） A .NET fluent validation library written in C# （页面存档备份，存于互联网档案馆） A tutorial for creating formal Java fluent APIs from a BNF notation （页面存档备份，存于互联网档案馆）