Object-Oriented PHP · Lesson 6 of 14

Constructors

Initialize required object state when constructing an instance.

Lesson

The __construct method runs when an object is created and is the natural place to require its initial dependencies or state. Constructor property promotion can reduce repetition. Reject invalid constructor input so every successfully created object begins in a valid state. This constructor requires a non-empty title before the object can be used. Further guidance Give an object one clear responsibility and protect state that must satisfy a rule. Prefer a small public contract and composition for replaceable collaborators; use inheritance only for a genuine subtype. Test behavior through public methods instead of relying on internal implementation details. Practice task: Create a fresh example for Constructors. Predict the result before running it, then change one input and explain why the result changes. Test a normal case and one boundary or invalid case where it applies. Compare your output with the example and note one rule you would use in a real project.

Code examples

Constructors

PHP

class Article
{
    public function __construct(public string $title) {}
}
$article = new Article('Learning PHP');
echo $article->title;

Expected output

Learning PHP

Key points

Initialize required object state when constructing an instance.
Protect object invariants behind a small public API.
Prefer composition unless inheritance expresses a genuine subtype.

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