Namespace, Trait, and Use in PHP - php

Question

I have been trying to use and understand namespace and traits but getting this error:
"Trait a\b\Train not found" when I run example.php
"Trait a\b\Train not found" when I run Bayes.php
Just confused how it works and why getting error.
Here my code:
(these files store in the same folder)
//example.php
use a\classification;
include_once 'Bayes.php';
$classifier = new Bayes();
$classifier -> train($samples, $labels);
$classifier -> predict([something]);
//Bayes.php
namespace a\classification;
use a\b\Predict;
use a\b\Train;
class Bayes {
use Train, Predict
}
//Train.php
namespace a\b;
trait Train{
}
//Predict.php
namespace a\b;
trait Predict{
}
I'm sorry for my dumb question, really appreciate for your help :"

Answer 1

You first need to include Train.php and Predict.php inside Bayes.php. You're referring to the traits, but how does PHP know about those?
Then, you need to specify a proper namespace when creating a new Bayes(). You include the file, but it's in another namespace. The use declaration at the top isn't doing much. It lets you create a new classification\Bayes() instead of new a\classification\Bayes().
Try something like this instead:
example.php
<?php
use a\classification\Bayes;
include_once 'Bayes.php';
$classifier = new Bayes();
$samples = "text";
$labels = "text";
$classifier -> train($samples, $labels);
$classifier -> predict(["something"]);
Bayes.php
<?php
namespace a\classification;
require_once 'Train.php';
require_once 'Predict.php';
use a\b\Predict as P;
use a\b\Train as T;
class Bayes
{
use T, P;
}
Train.php
<?php
namespace a\b;
trait Train
{
public function Train()
{
echo "training";
}
}
Predict.php
<?php
namespace a\b;
trait Predict
{
function predict()
{
echo "predicting";
}
}
Note the use of an alias in Bayes.php: use a\b\Predict as P; This is where aliases can be helpful to simplify code. If the alias isn't specified, it just uses the last name without namespaces.

Answer 2

You're running into trouble because you're not requiring the files you need, so PHP doesn't know what you're talking about when you ask it to use some of these classes.
example.php requires access to Bayes.php
use a\classification;
require_once 'Bayes.php';
Bayes.php requires access to Train.php and Predict.php
namespace a\classification;
require_once 'Train.php';
require_once 'Predict.php';
use a\b\Predict, a\b\Train;
class Bayes {
use Train, Predict
}
Note: use require_once rather than include_once when the external resource is necessary.