Fluent interface

In software engineering, a fluent interface (as first coined by Eric Evans and Martin Fowler) is an implementation of an object oriented API that aims to provide more readable code.

A fluent interface is normally implemented by using method cascading (concretely method chaining) to relay the instruction context of a subsequent call (but a fluent interface entails more than just method chaining ). Generally, the context is

The term "fluent interface" was coined in late 2005, though this overall style of interface dates to the invention of method cascading in Smalltalk in the 1970s, and numerous examples in the 1980s. A common example is the iostream library in C++, which uses the << or >> operators for the message passing, sending multiple data to the same object and allowing "manipulators" for other method calls. Other early examples include the Garnet system (from 1988 in Lisp) and the Amulet system (from 1994 in C++) which used this style for object creation and property assignment.

There are many examples of JavaScript libraries that use some variant of this: jQuery probably being the most well known. Typically fluent builders are used to implement 'database queries', for example in https://github.com/Medium/dynamite :

A simple way to do this in JavaScript is using prototype inheritance and `this`.

The jOOQ library models SQL as a fluent API in Java

The op4j library enables the use of fluent code for performing auxiliary tasks like structure iteration, data conversion, filtering, etc.

The fluflu annotation processor enables the creation of a fluent API using Java annotations.

The JaQue library enables Java 8 Lambdas to be represented as objects in the form of expression trees at runtime, making it possible to create type-safe fluent interfaces, i.e. instead of:

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