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class UserCollection {
    /** @var User[] */
    private array $items = [];
 
    public function add(User $user): void {
        $this->items[] = $user;
    }
 
    public function all(): array {
        return $this->items;
    }
}

Now let's slow everything down — really down — and explain every new symbol, keyword, and idea.

1. class UserCollection { ... }

This defines a new class named UserCollection (any name).
Think of it as: “a special box designed to hold many User objects”.
It's not a user.
It's not an entity.
It's not a value object.
It's a collection — a group of things that belong together.

2. /** @var User[] */ — the docblock annotation

This is a hint for humans and tools.

It says:
“Inside this property, we expect an array of User objects”.

It doesn't change how PHP runs.
It helps:

• your editor
• static analysis tools
• future readers
• your own brain

It's a label on the box saying:
“This box contains Users”.

3. private array $items = [];

This line introduces several new ideas:

private
This means:
“Only this class can touch this property”.
No one outside the collection can directly modify $items.
This protects the collection from accidental misuse.

array
This is the type.
It tells PHP:
“This property must always be an array”.

$items
This is the actual property name — the internal storage.

= [];
This initializes the property as an empty array.

So the whole line means:

"Inside this collection, 
keep a private array named $items, 
starting empty".

4. public function add(User $user): void { ... }

This is a method — a small action the collection can perform.

Let's break it down:

public — Anyone can call this method.

function add(…)
The method is named add — meaning “add something to the collection”.

User $user
This is a typed parameter.
It means:
“You must pass a User object here. Nothing else is allowed”.
This is where type safety begins.

: void
This means:
“This method does not return anything”.
It performs an action but gives nothing back.

5. $this->items[] = $user;

This is the heart of the method.

Let's break it down:

$this
Means: “the current object we're inside”.

In our metaphor: “this box”.

→items
Means: “open the box and look at the $items property inside”.

[] = This is PHP's way of saying: “append this item to the end of the array”.

$user
The object we're adding.

So the whole line means:

"Open this collection's internal array 
and append the user to it".

6. public function all(): array { ... }

This method returns the entire collection.

public
Anyone can call it.

all()
A simple, readable name meaning: “give me everything”.

: array
This method returns an array. return $this→items;
Give back the internal list.

So the method means:

"Return the full list of users stored inside this collection".

—-

Here's the whole class in plain English:

• UserCollection is a named box for holding many User objects.
• It keeps its internal list private so nothing can break it accidentally.
• It provides an add() method to safely insert a User.
• It provides an all() method to retrieve the full list.
• It guarantees that only User objects can be added.
• It gives your code predictable behavior and clear meaning.

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