PHP 7.4 Changes

PHP 7.4 brought typed properties, arrow functions, null-coalescing assignment, and array unpacking. It also deprecated curly-brace array and string offsets, which commonly appear in older projects.

Changes Worth Recognising

• Typed properties make uninitialised state visible; they are not automatically null.
• Arrow functions capture outer variables by value.
• ??= assigns a default only when the target is absent or null.
• Curly-brace offsets such as $name{0} need replacement with square brackets.

Representative Code

<?php

$products = [
    ['name' => 'Notebook', 'price' => 500],
    ['name' => 'Pen', 'price' => 150],
];

$names = array_map(fn(array $product): string => $product['name'], $products);
echo implode(', ', $names) . PHP_EOL;

// Prints:
// Notebook, Pen

Upgrade Review

• Initialise typed properties before reading them.
• Search for curly-brace offsets before upgrading.
• Check arrow functions that need mutation: capture-by-value may not match the intended behaviour.

Typed properties are the most consequential change here because they expose previously hidden object-state errors.