流式接口 fluent interface

wiki：https://www.wikiwand.com/zh/%E6%B5%81%E5%BC%8F%E6%8E%A5%E5%8F%A3

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（英语：enmethod cascading） (具体说是方法链式调用（英语：method chaining）)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（英语：enmethod cascading）。

例子

PHP

In PHP, one can return the current object by using the $this special variable which represent the instance. Hence return $this; will make the method return the instance. The example below defines a class Employee and three methods to set its name, surname and salary. Each return the instance of the Employee class allowing to chain methods.

<?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

JavaScript

用于数据库查询的jQuery，例如https://github.com/Medium/dynamite :

// 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使用原形继承与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();