Scalar Type Declarations (PHP 7.0)

TL;DR

Explanation

PHP 7.0 (December 2015) added scalar type hints: int, float, string, bool. With declare(strict_types=1): strict enforcement — wrong type throws TypeError. Without it: PHP coerces where possible ('5' → 5). Return types also added: function add(int $a, int $b): int. This enabled PHPStan, Psalm, and IDE analysis to verify type contracts. Previously only class/interface names and array/callable were valid hints. PHP 7.1 added nullable types (?string), PHP 7.1 added void return. PHP 8.0 added union types (int|string), PHP 8.1 added never.

Common Misconception

Why It Matters

Common Mistakes

• Not using declare(strict_types=1) — coercion hides type bugs.
• Forgetting to add return types — functions without return types can't be fully analysed.
• Using mixed instead of proper union types — loses all type safety.

Code Examples

// PHP 5 — no type hints:
function add($a, $b) {
    return $a + $b; // What if strings are passed?
}

<?php declare(strict_types=1);

function add(int $a, int $b): int {
    return $a + $b;
}

function greet(?string $name): string {
    return 'Hello, ' . ($name ?? 'World');
}

References

• ↗ https://www.php.net/manual/en/migration70.new-features.php

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