Why does 'composer dumpautoload -o' fix 'Class not found' PHP error? - php

Question

I have a Laravel 5.8 project that is dependent on a private package.
When I run composer install the package is installed and shows up in the vendor folder.
project composer.json
{
...
"require": {
"php": ">=7.0",
"company/api-request": ">=1.0.0"
}
...
}
package src/ApiRequest.php
<?php
namespace Company;
class APIRequest
{
...
}
package composer.json
{
...
"autoload": {
"psr-4": {
"Company\\": "src/"
}
}
...
}
When I call the package
\Company\APIRequest::run();
I am getting
Message: Class 'Company\APIRequest' not found
I know the PHP syntax is correct because when I run composer dumpautoload -o the error is gone, but why is it necessary?
I expect composer install or composer update should be sufficient; I have no problem with external packages.
Am I missing anything here?

Answer 1

If the class name and file name don't match, that would cause the auto-loading to not work since that is a requirement with PSR-4. From the docs:
The terminating class name corresponds to a file name ending in .php. The file name MUST match the case of the terminating class name.
If that's the case, composer dumpautoload -o is probably working around this for you, see this Reddit post:
The reason -o works, is Composer creates a giant associative array where classname = filename