Object-Oriented PHP · Lesson 13 of 14

Static Members

Use static members for behavior or state associated with a class.

Lesson

Static methods and properties belong to the class rather than one particular instance. They can suit pure utility behavior or named constructors, but global mutable static state makes tests and concurrency harder. Prefer instance dependencies when behavior needs configuration or substitution. This static method is pure: its result depends only on its argument. 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 Static Members. 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

Static Members

PHP

class Slug
{
    public static function from(string $title): string
    {
        return strtolower(str_replace(' ', '-', trim($title)));
    }
}
echo Slug::from('PHP Basics');

Expected output

php-basics

Key points

Use static members for behavior or state associated with a class.
Protect object invariants behind a small public API.
Prefer composition unless inheritance expresses a genuine subtype.

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