computer programming Computer programming or coding is the composition of sequences of instructions, called computer program, programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by-step specifications of proc ...

, autoloading is the capability of loading and linking portions of a program from

mass storage In computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. In general, the term ''mass'' in ''mass storage'' is used to mean ''large'' in relation to contemporaneous hard disk drive ...

automatically when needed, so that the programmer is not required to define or include those portions of the program explicitly. Many high-level programming languages include autoload capabilities, which sacrifice some run-time speed for ease of coding and speed of initial compilation/linking. Typical autoload systems intercept

procedure call In computer programming, a function (also procedure, method, subroutine, routine, or subprogram) is a callable unit of software logic that has a well-defined interface and behavior and can be invoked multiple times. Callable units provide a p ...

s to undefined

subroutine In computer programming, a function (also procedure, method, subroutine, routine, or subprogram) is a callable unit of software logic that has a well-defined interface and behavior and can be invoked multiple times. Callable units provide a ...

s. The autoloader searches through a

path A path is a route for physical travel – see Trail. Path or PATH may also refer to: Physical paths of different types * Bicycle path * Bridle path, used by people on horseback * Course (navigation), the intended path of a vehicle * Desir ...

of directories in the computer's file system, to find a file containing

source Source may refer to: Research * Historical document * Historical source * Source (intelligence) or sub source, typically a confidential provider of non open-source intelligence * Source (journalism), a person, publication, publishing institute ...

object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an a ...

code that defines the subroutine. The autoloader then loads and links the file, and hands control back to the main program so that the subroutine gets executed as if it had already been defined and linked before the call. Many interactive and high-level languages operate in this way. For example, IDL includes a primitive path searcher, and

Perl Perl is a high-level, general-purpose, interpreted, dynamic programming language. Though Perl is not officially an acronym, there are various backronyms in use, including "Practical Extraction and Reporting Language". Perl was developed ...

allows individual modules to determine how and whether autoloading should occur. The

Unix shell A Unix shell is a Command-line_interface#Command-line_interpreter, command-line interpreter or shell (computing), shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command languag ...

may be said to consist almost entirely of an autoloader, as its main job is to search a path of directories to load and execute command files. In

PHP PHP is a general-purpose scripting language geared towards web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by the PHP Group. ...

5, autoload functionality is triggered when referencing an undefined

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

. One or more autoload functions—implemented as the __autoload magic function or any function registered to the SPL autoload stack—is called and given the opportunity to define the class, usually by loading the file it is defined in.

PHP

spl_autoload_register(function ($class) { $file = 'src/' . str_replace('\\', '/', $relative_class) . '.php'; if (file_exists($file)) { require $file; } });

External links

PSR-4
Improved Autoloading Standard
Autoloading Classes
in PHP
spl_autoload_register
in PHP Programming constructs