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An even more in depth article can be found here on WPKrauts.

EDIT The obviously correct way is to use namespaced code, prepared for PSR-4 autoloading by putting everything in the appropriate directory that already is defined via the namespace. Then just use Composer and a composer.json to manage your dependencies and let it auto-build your PHP autoloader (that imports automatically a file by just calling use \<namespace>\ClassName). That's the de-facto standard in the PHP world, the easiest way to go and even more pre-automated and simplified by WP Starter.

EDIT The obviously correct way is to use namespaced code, prepared for PSR-4 autoloading by putting everything in the appropriate directory that already is defined via the namespace. Then just use Composer and a composer.json to manage your dependencies and let it auto-build your PHP autoloader (that imports automatically a file by just calling use \<namespace>\ClassName). That's the de-facto standard in the PHP world, the easiest way to go and even more pre-automated and simplified by WP Starter.

EDIT The obviously correct way is to use namespaced code, prepared for PSR-4 autoloading by putting everything in the appropriate directory that already is defined via the namespace. Then just use Composer and a composer.json to manage your dependencies and let it auto-build your PHP autoloader (that imports automatically a file by just calling use \<namespace>\ClassName). That's the de-facto standard in the PHP world, the easiest way to go and even more pre-automated and simplified by WP Starter.

Summed up

An even more in depth article can be found here on WPKrauts.