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How does PSR-4 autoloading work, and how does it map a namespace structure directly to a corresponding directory structure on disk? What is the difference between using a relative namespace reference, a fully qualified name starting with a backslash, and importing a class with use, when referencing a class from within a namespaced file? How do you organize namespaces effectively in a larger application to reflect logical groupings such as models, services, and controllers? How does Composer's classmap and files autoloading mechanism differ from PSR-4, and when would you use these alternative approaches instead?
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How does Composer generate and optimize its autoloader for production, and what is the difference between the development autoloader and an optimized production autoloader?

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During development, Composer's autoloader typically does some work at runtime to determine exactly which file corresponds to a given class based on the configured PSR-4 rules, but running composer dump-autoload with the optimize flag, which also happens automatically when installing with the no dev flag, generates a fully precomputed classmap mapping every class directly to its file, eliminating that runtime resolution overhead entirely and providing a measurable performance improvement, which is why production deployments should always use this optimized autoloader.
composer install --no-dev --optimize-autoloader
Real-world example A production deployment pipeline always runs composer install with the optimize autoloader flag, ensuring the live application benefits from Composer's fully precomputed class map rather than the slightly slower runtime resolution used during local development.

Common follow-ups: How much of a measurable performance difference does the optimized autoloader typically provide?;Does the optimized autoloader need to be regenerated every time new classes are added during development?

Deployment & Hosting for PHP Applications;Performance Optimization & OPcache
All 7 Namespaces & Autoloading questions