Predefined Interfaces and Classes
PHP Manual

The Stringable interface

Introduction

The Stringable interface denotes a class as having a __toString() method. Unlike most interfaces, Stringable is implicitly present on any class that has the magic __toString() method defined, although it can and should be declared explicitly.

Its primary value is to allow functions to type check against the union type string|Stringable to accept either a string primitive or an object that can be cast to a string.

Interface synopsis

Stringable
/* Methods */
public string Stringable::__toString()

Stringable Examples

Example #1 Basic Stringable Usage

This uses constructor property promotion.

<?php
class IPv4Address implements Stringable {
    public function __construct(
        private string $oct1,
        private string $oct2,
        private string $oct3,
        private string $oct4,
    ) {}

    public function __toString(): string {
        return "$this->oct1.$this->oct2.$this->oct3.$this->oct4";
    }
}

function showStuff(string|Stringable $value) {
    // For a Stringable, this will implicitliy call __toString().
    print $value;
}

$ip = new IPv4Address('123', '234', '42', '9');

showStuff($ip);
?>

The above example will output something similar to:

123.234.42.9

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