辅助函数应该属于一个类吗？

In my efforts to rewrite a past project of mine with OOP in mind, I have broken my code up into classes such as Devices, Facilities, etc.

Before moving to a more object oriented approach, I just stuck all of my helper functions in an included "functions.php" file. Using Devices as an example, would it be best to have a Devices class for my object specific properties/methods, then have a DeviceManager class to store functions like getDeviceByName, getDeviceByID, etc?

From what I am understanding, OOP is more about readability/manageability than anything else, why I assume the purpose would just be to have something like DeviceManager::GetDevice("Computer1") in place of GetDeviceByName("Computer1")

In a OOP languages like C# or Java, you simply can't have functions outside a class, so there's no issue. That doesn't mean you're doing OOP, which is a mindset.

In PHP you can either put the relevant functions into a nampespace or within a class (inside a namespace). It's up to you, there's no right or wrong approach. Personally, I'd put them into a class because that's how I'm doing it in C# and it'll help a bit with productivity: I group related functionality in one place (class). It's easier to manage.

But strictly from a programming point of view, there's no difference, your code won't be cleaner/decoupled or more OOP because you've put functions into a class or namespace

A few advantages when using Namespace or Class for static functions.

  1. Namespace and Class Name helps distinguish functions. You can avoid naming conflicts.

  2. DPDate::FirstDayOfMonth() is better than FirstDayOfMonth() when you want to take advantage of auto suggestion of the IDE.

  3. It is really all about cohesion and decoupling.

You must following this rules:

  1. In OOP you MUST ALWAYS use a CLASS
  2. Your method must have a single responsability
  3. Avoid generic helper classes, classes must have a simple and specific responsability
  4. Don't use static methods, use strategy (pass the object throw the param) to call a method, this way you can create a Mock to test your methods.
  5. Avoid private methods, this make dificult to test your classes

Keep this things in mind, and you will gona make a clean code. =)

Answering Eric about item 4: This code it will use static method:

public function myFunction() {
    $deviceId = DeviceManger::getDeviceId('computer 1');
    // Rest of code using the device id 
}

This way i cant mock the return of Device ID, this way i can:

public function myFunction(deviceManger) {
    $deviceId = deviceManager->getDeviceId('computer 1');
    // Rest of code using the device id 
}

The code with mock in test function:

$deviceManager = $this->getMock('DeviceManager');
$deviceManager->method('getDeviceId')->returnValue(1);
myFuncion($deviceManager);

If you are thinking of using a class as a namespace then you can just as well use an actual namespace:

namespace MyCollectionOfFunctions;
function printMyName($name) {
    echo $name;
}

And then you can use the functions like this:

use MyCollectionOfFunctions as fn;
echo fn\printMyName('Brett Powell');

There is nothing wrong with functions. Do not let anyone tell you that they belong is a class, as static methods. It can be done that way, but since we got namespaces there really is no reason for it.