overload2
Elegant solution for function overloading in JavaScript.
When you are tired with writing tasteless code to do with arguments, overload2 will 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
Links
Get Started
Install overload2 firstly.
npm install overload2 --save
Open node and run next code:
const overload2 = require('overload2');
var getDay = overload2()
.overload(
Date,
function foo(d) { return d.getDay(); }
)
.overload(
'string',
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(
2,
function md(month, date) {
var d = new Date;
return d.setMonth(month - 1), d.setDate(date), d.getDay();
}
)
.overload(
'*', Date, '*',
function select(some, d, others) {
return d.getDay();
}
)
;
getDay(new Date);
getDay('2000-1-1');
getDay(2000, 1, 1);
getDay(12, 1);
getDay('foo', 'bar', new Date, 'quz');
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. [0,1]
is matched with Array
. See another example:
var getDay = overlaod2()
.overload(Date, function foo(d) { return d.getDay(); })
.overload(String, function bar(s) { return new Date(s).getDay(); })
;
getDay(new Date);
getDay(new String('2000-1-1'));
Customized Datatype
You may create customized datatypes by new overload2.Type(fn)
, e.g.
var MonthName = new overload2.Type(function(value) {
var names = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
return names.indexOf(value) >= 0;
});
var getDay = overlaod2()
.overload(Date, function foo(d) { return d.getDay(); })
.overload('number', MonthName, 'number', function() {
return new Date(year, month - 1, date).getDay();
})
;
getDay(2000, 'Jan', 1);
Predefined Datatype
Predefined Data Type | Remark |
---|
overload2.Type.ANY | Anything. |
overload2.Type.BOOLEAN | It must be true or false , anything else including instance of Boolean is unmatched. |
overload2.Type.CHAR | A string whose length equals 1, e.g. "a" |
overload2.Type.NUMBER | A number, but NOT instance of Number . |
overload2.Type.SCALAR | A number, string or boolean, but NOT instance of Number , String or Boolean . |
overload2.Type.STRING | A string, but NOT instance of String . |
ATTENTION:
-
Predefined datatypes named Type.BOOLEAN
, Type.NUMBER
and Type.STRING
refers to primitive values with types of boolean
, number
and string
, not their Object-wrapped forms. If Object-wrapped form required, just directly use constructor functions Boolean
, Number
and String
as datatype, see Datatypes: Constructor Function.
-
Before version 0.1.0, predefined datatypes are appended directly to the overload2
module. To avoid ambiguity in future, predefined datatypes will be appended to overload2.Type
. Although the old ones reserved, it's strongly suggested not to use overload2.<PREDEFINED_TYPE_NAME>
any longer.
Datatype Alias
ATTENTION: Datatype aliases are CaseSensitive strings.
Alias | Corresponding Datetype |
---|
? | overload2.Type.ANY |
any | overload2.Type.ANY |
boolean | overload2.Type.BOOLEAN |
char | overload2.Type.CHAR |
number | overload2.Type.NUMBER |
object | overload2.Type.PLAIN_OBJECT |
scalar | overload2.Type.SCALAR |
string | overload2.Type.STRING |
Create Datatype With Factory Method
overload2 offers some factory methods to create frequently used datatypes, e.g. enum.
-
overload2.Type.enum(item [, ...])
Return an enumeration type.
-
overload2.Type.and(type1, type2 [, ...])
Create a compound type.
-
overload2.Type.or(type1, type2 [, ...])
Create a compound type.
-
overload2.Type.not(type)
Create a new type which is complementary to the origin type.
Mutable Parameter
By appending size decorator, we can define mutable parameters. E.g.
var add = overload2()
.overload('number *', function(numbers) {
var ret = 0;
numbers.forEach(function(number) { ret += number; })
return ret;
})
.overload('boolean {2,3}', function(bools) {
var ret = false;
for (var i = 0; !ret && i < bools.length; i++) {
ret = bools[i];
}
return ret;
})
.overload([ Date, '+' ], function(dates) {
var date = dates[0];
for (var i = 1; i < dates.length; i++) {
if (date < dates[i]) {
date = dates[i];
}
}
return date;
})
;
Size decorators look like repetition in regular expression. Here are some examples for overload param with size decorators:
[ Date, '{2,}']
'number *'
'*'
'+'
'?'
'{2}'
'{2,4}'
'{2,}'
'{,4{}'
'2'
'2,4'
'2,'
',4'
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
overload2(), Create An Overloaded Function
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.
class 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
.
class 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()
.
class 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()
.
class overload2.Overload
-
new overload2.Overload( number , function <implementation> )
Create an Overload
instance by restricting the number of arguments.
-
new overload2.Overload( ParamList, function <implementation> )
Create an Overload
instance bound to specified ParamList
.
-
new overload2.Overload( <param> [ , ... ] , function <implementation> )
Create an Overload
instance with optional definitions of Param
.
-
new overload2.Overload(function <implementation> )
Create an Overload
instance which will be invoked while arguments length equals 0.
-
Overload overload2.Overload.parse( ? )
Arguments suitable for new Overload()
are also suitable for the Overload.parse()
.
class 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> [ , Boolean ] )
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.
-
Unit Test
Another way to understand overload2 is via reading unit-test code. To run the unit test on the local installed module, please:
cd node_modules/overload2
npm intall
npm test
-
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
There have been dozens of packages devoted to function overloading in JavaScript, and some of them are really not bad, e.g.
So, is overload2 redundant? I donnot know. Each of previous is unsatisfactory more or less, of course overload2 is not perfect either. Maybe future ECMAScript specification will support function overloading. However, until then, I will depend on overload2 while coding in JavaScript.
Honorable Dependents
Welcome to be the first dependent of overload2!
About
Why postfixed the package name with number 2? Since name "overload" has been occupied, inspired by well-known package "pm2" and "through2", I thought "overload2" is not bad. The most important reason why I choose "overload2" was because 2 /tu:/ is pronounced like tool /tu:l/.
References