Composer Dependency Manager

Composer is an application-level dependency manager for the PHP programming language, designed to simplify the process of managing and installing external libraries a project requires. By defining all necessary packages and their version constraints in a `composer.json` configuration file, developers can use Composer to automatically download the correct files from the main repository, Packagist, into a `vendor` directory. This process also generates a `composer.lock` file to ensure consistent library versions across all development and production environments, and it conveniently handles class autoloading, making it seamless to integrate and use the third-party code.

1. Introduction to Dependency Management
   1. Understanding Software Dependencies
      1. Definition and Purpose of Dependencies
      2. Types of Dependencies
         1. Direct Dependencies
         2. Transitive Dependencies
         3. Development Dependencies
         4. Optional Dependencies
   2. Problems with Manual Dependency Management
      1. Version Conflicts and Incompatibilities
      2. Dependency Hell
      3. Manual Updates and Maintenance Overhead
      4. Lack of Reproducible Builds
      5. Security Vulnerability Tracking
   3. Role and Benefits of Dependency Managers
      1. Automated Dependency Resolution
      2. Version Management and Constraints
      3. Reproducible Build Environments
      4. Security Vulnerability Detection
      5. Simplified Project Setup
   4. Dependency Management Across Programming Languages
      1. npm for JavaScript
      2. pip for Python
      3. Maven for Java
      4. NuGet for .NET
      5. Cargo for Rust
   5. Composer in the PHP Ecosystem
      1. History and Development of Composer
      2. Impact on Modern PHP Development
      3. Relationship with PEAR and Other PHP Tools
      4. Community Adoption and Standards