overload2

overload2

Elegant solution for function overloading in JavaScript.

Tied with writing tasteless code to do with arguments? Use overload2 to make things easy.

On programming with strongly-typed languages such as C++ and Java, function overloading is frequently employed to make API more convenient to be used. As a weakly-typed language, JavaScript does not support function overloading. At the same time, fortunately, functions in JavaScript may be passed with any arguments that is why overload2 is feasible.

Table of contents

• Get Started
• Datatypes
• Move Forward
• APIs
• Examples
• Why overload2

See CHANGE LOG for notable changes. Or access project's homepage for latest updates.

Get Started

Install overload2 firstly.

npm install -g overload2

Open node and run next code:

const overload2 = require('overload2');

// Create a function with overloaded implementations.
var getDay = overload2()
	// Create an overloaded implementation with method overload().
	// The last argument is the implementation function,
	// and the previous is/are used to qualify the datatypes or number of real arguments.
	.overload(
		Date, // consturctor function
		function foo(d) { return d.getDay(); }
	)
	.overload(
		'string', // predefined datatype
		function bar(s) { return new Date(s).getDay(); }
	)
	.overload(
		'number', 'number', 'number',
		function quz(year, month, date) { return new Date(year, month - 1, date).getDay(); }
	)
	.overload(
		4, // length of arguments
		function four() { console.log('too many arguments'); }
	)
	;

getDay(new Date);
// foo(d) invoked

getDay('2000-1-1');
// bar(s) invoked

getDay(2000, 1, 1);
// quz(year, month, date) invoked

getDay(1, 2, 3, 4);
// four() invoked

Datatypes

According to overload2 , there are different ways to define a datatype.

Constructor Function

overload2 can match any instance with its constructor function, e.g

var getDay = overlaod2()
	.overload(Date, function foo(d) { return d.getDay(); })
	.overload(String, function bar(s) { return new Date(s).getDay(); })
	;

getDay(new Date);  // foo() invoked
getDay(new String('2000-1-1'));  // bar() invoked

for example [0,1] is matched with Array.

Customized Datatype

You may create customized datatypes by new overload2.Datatype(fn), e.g.m

var DAYNAME = new overload2.Type(function(value) {
	var names = ['sun', 'mon', 'tue', 'wed', 'thu', 'fri', 'sat'];
	return names.indexOf(value) >= 0;
});

Predefined Datatype

Predefined Data Type	Remark
overload2.ANY	Anything.
overload2.BOOLEAN	It must be true or false, anything else including instance of Boolean is unmatched.
overload2.CHAR	A string whose length equals 1, e.g. "a"
overload2.NUMBER	A number, but NOT instance of Number.
overload2.SCALAR	A number, string or boolean, but NOT instance of Number`, StringorBoolean``.
overload2.STRING	A string, but NOT instance of String.

Datatype Alias

ATTENTION: Datatype aliases are CaseSensitive.

Alias	Corresponding Datetype
*	overload2.ANY
any	overload2.ANY
boolean	overload2.BOOLEAN
char	overload2.CHAR
number	overload2.NUMBER
scalar	overload2.SCALAR
string	overload2.STRING

Create Datatype With Factory Method

overload2 offers some factory methods to create frequently used datatypes, e.g. enum.

• overload2.enum(item[, ...])
  Return Datatype instance

Move Forward

Beyond the basic use, overload2 is also suitable with more complex and large-scale programs. See the class hierarchy shown below:

The usage of classes in overload2 is explained in the next table:

Class	Remark
overload2.OverloadedFunction	wrapper of overloaded function, not a function instance itself
overload2.Overload	to define overloading implementation
overload2.ParamList	to define a parameter list
overload2.Param	to define a parameter
overload2.Type	wrapper of class (consturctor function), or to customise some datatype

Instances of Type, Param, ParamList and Overload are able to be created independently and be re-used in creating instances of superior class(es).

Here is an example for advanced mode.

APIs

Overloaded Function Instance

overload2 itself is a function, when invoked, it will return an overloded function instance.

• <fn> overload2()
  Create a new overloaded function. The function has no implementations before .overload() called.

• <fn> <fn>.overload( [ <datatype>, ... ] function <implementation> )
  Append an overloading implementation to existing overloaded function.

• <fn> <fn>.default( function <implementation> )
  Set default implementation function for existing overloaded function.

overload2.Type

To define a datatype in context of overload2, there are different ways including overload2.Type. And all other datatypes will be converted to instances of overload2.Type before being used.

• new overload2.Type( function | RegExp <matcher> )
  Here matcher may be a function or RegExp object.

• private boolean <type>.match( <value> )
  Return true if value matches the datatype, otherwise return false.

overload2.Param

A Param is made up of a Type and some decorators. Available decorators are:

Decorator	Remark
null	If argument equals null, it matches the parameter.
undefined	If argument equals undefined (the place should be occupied), it matches the parameter.

• new overload2.Param( string "<alias> <decorator> ..." )
  The alias should be one of alias listed in table Datatype Alias.

• new overload2.Param( Type | function | string <datatype>, string <decorator(s)> [ , string <decorator(s)> ] )
  Here datatype may be instance of Type, or construtor function, or datatype alias.

• private boolean <param>.satisfy( <value> )
  To judge if the argument value satisfy the parameter.

• Param overload2.Param.parse( ? )
  Arguments suitable for new Param() are also suitable for the Param.parse().

overload2.ParamList

• new overload2.ParamList( [ Param | Array | String <param> [ , ... ] ] )
  Here param may be an instance of Param, or a string or an array which may used as argument(s) for new Param().

• private boolean <paramList>.satisfy( Array | Arguments <args> )
  To check arguments with parameters, return true if matched or false if not.

• ParamList overload2.ParamList.parse( ? )
  Arguments suitable for new ParamList() are also suitable for the ParamList.parse().

overload2.Overload

• new overload2.Overload( number , function <implementation> )

• new overload2.Overload( ParamList, function <implementation> )

• new overload2.Overload( [ <param>, [ ..., ] ] function <implementation> )

• Overload overload2.Overload.parse( ? )
  Arguments suitable for new Overload() are also suitable for the Overload.parse().

overload2.OverloadedFunction

• new overload2.OverloadedFunction()
  The instance of OverloadedFunction is a wrapper, not a function itself.

• <wrapper>.exec( ... )
  Run the overloaded function.

• <wrapper>.apply( <scope>, Array | Arguments <args> )
  Run the overloaded function under specified scope, passing arguments as an array or Arguments instance.

• <wrapper>.call( <scope> [ , <arg> [ , ... ] ] )
  Run the overloaded function under specified scope, passing arguments one by one.

• <wrapper>.overload( Overload <overloadInstance> )
  Append an overloading implementation.

• <wrapper>.overload( ? )
  Append an overloading implementation, arguments suitable for new Overload() are also suitable for the <wrapper>.overload().

Examples

• Basic Usage
  To create overloaded function in simple way.

• Overloaded Constructor Function
  Overloaded function created by overload2 may also be used as class constructor.

• Run Overloaded Function Under Specified Scope
  A function created by overload2 may also be invoked by .apply(), .call(), as normal functions do. And, it may also be bound to specified scope with .bind().

• Advanced Usage
  Use overload2 in complex situations.

Why overload2

To be continued.

Changelog

[0.0.3] - 2017-05

overload2() will create a new overloaded function. Before, in v0.0.2, the overloaded function may be appended with an implementation meanwhile being created, if overload2() is called with arguments. This pattern is not only ambiguous, but also restrict the future expandability of overload2 (arguments passed to overload2() SHOULD be used to define attributes concerned with overloading, instead of specific implementation). So, since this version, overload2() will return an overloaded function WITHOUT ANY IMPLEMENTATION. And programmers must implement it by calling .overload() method.