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With code reuse comes the problem of dependency management, historically a rather manual and error-prone process. Fortunately, recent years have seen most programming languages solve this problem by introducing various tools for dependency management. In the PHP ecosystem, Composer become the standard thanks to its ease of use, flexibility, and wide adoption.
Even though Composer was built for dependency management, you can also use it for tasks like:
Autoloading: Automatically load classes and functions from external libraries to make them readily accessible from your code and simplify the process of integrating external code into your project.