Where to put plain object classes?

easiest way:

put it into the application/libraries folder
autoload this library in your application/config/autoload.php

then from anywhere in your controllers/models user: $this->library_name_here->some_function();

from other libraries in application/libraries or from helper files: $ci = get_instance(); $ci->library_name_here->some_function();

I really must contest that this is the 'easiest' way. This approach seems totally silly to me for the reasons I pointed out above:
* What if a class is only to be used statically. I.e., you NEVER instantiate this class for any reason because all of its methods are static.
* What if you must supply arguments to the constructor for the class? This would in all likelihood cause a fatal error if CodeIgniter tried to instantiate the object without providing these parameters.
* What if I need multiple instances of MyClass to perform some operation. E.g.:

Code:

$player1 = new Player("Mutt", $foo);
$player2 = new Player("Jeff, $bar);

In that case, why on earth would I tolerate the overhead of CI trying to instantiate the object??

ivantcholakov seems to have the most helpful suggestions in this matter. I agree that an autoloader is extremely useful for eliminating thickets of require/include statements. It's been my experience that these include/require statements are the source of much code redundancy and many bugs.

As for using Composer, I am not familiar with it, but that seems to me to introduce a completely unnecessary dependency and additionally requires one to maintain composer.json as well each time one adds additional classes or libraries. Perhaps I'm missing something.