Composer

A Dependency Manager for PHP

Composer is an application-level package manager for the PHP programming language that provides a standard format for managing dependencies of PHP software and required libraries. It was developed by Nils Adermann and Jordi Boggiano in 2012, who continue to manage the project.

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To install composer in windows download and install executable file
https://getcomposer.org/download/

To install in ubuntu

apt install composer

To install latest version of composer on ubuntu

cd ~
curl -sS https://getcomposer.org/installer -o composer-setup.php

sudo php composer-setup.php --install-dir=/usr/bin --filename=composer

OR

sudo php composer-setup.php --install-dir=/usr/local/bin --filename=composer

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composer.json
Keep this file in the project’s root directory
NOTE: This file is mandatory to in root directory to use composer as composer look for this file when you run dump-autoload

{
	"autoload" : {
		"files" : ["lib/global_functions.php"],
	}
}

lib/global_functions.php

function getMessage() {
	
	echo "Hello World" . PHP_EOL;

}

Create autoload file by running any one following command

composer dump-autoload
composer dump-autoload -o

index.php

<?php
require("vendor/autoload.php");
echo "=====================\n";
getMessage();

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How to autoload classes using composer

app/admin/Account.php

<?php
namespace App\Admin;

class Account {
	//this is magic method as it will invoked automatically 
        //when you create instance of account
	public function __construct() {
		
		echo "I am from Admin Account" . PHP_EOL;
	}
}

app/user/Account.php

<?php
namespace App\User;

class Account {
	//this is magic method as it will invoked automatically 
	//when you create instance of account
	public function __construct() {
		echo "I am from User Account" . PHP_EOL;
	}	
}

modify composer.json

{
	"autoload" : {
		"files" : ["lib/global_functions.php"],
		"classmap" : ["app"]
	}
}

Once you modify composer.json file run dump-autoload command again to add classmapping in autoload file

composer update

OR

composer dump-autoload -o

modify index.php

<?php

require("vendor/autoload.php");

echo "=====================\n";

getMessage();

echo "=====================\n";

new App\User\Account();

echo "=====================\n";

new App\Admin\Account();

echo "=====================\n";

Ref Code: https://gitlab.com/codeinsightacademy/composer-demo.git