PHP 5.5: Major Features

PHP 5.5 makes memory-friendly iteration mainstream with generators (yield), adds finally to try/catch, introduces a proper password API (password_hash, password_verify, password_needs_rehash), and adds everyday helpers like array_column() and the ClassName::class constant. It also ships Zend OPcache (when built/enabled), which changes performance characteristics of production workloads. Migration work often focuses on subtle foreach/list() behavior and finishing mysql → mysqli/PDO moves.

Anchor your checklist to migration55.

Table of Contents

Generators (yield)

Generators compute values on demand instead of building giant arrays:

function lines($path)
{
    $fh = fopen($path, 'rb');
    try {
        while (($line = fgets($fh)) !== false) {
            yield rtrim($line, "\r\n");
        }
    } finally {
        fclose($fh);
    }
}

Use for large CSV/LOG streaming and cooperative iterators.

finally

Runs always after try/catch—ideal for closing resources even when return or exceptions occur.

Password hashing API

$hash = password_hash($plain, PASSWORD_DEFAULT);
if (password_verify($plain, $hash)) {
    if (password_needs_rehash($hash, PASSWORD_DEFAULT)) {
        $hash = password_hash($plain, PASSWORD_DEFAULT);
    }
}

Stop hand-rolling salt and cost unless you must interoperate with legacy schemes.

array_column() & ::class

  • array_column($rows, 'email', 'id') extracts columns from result sets.
  • SomeClass::class resolves to the fully qualified class name string—refactor-safe vs string literals.

OPcache

When enabled, OPcache caches bytecode—after deploys, coordinate opcache_reset() or process reloads so changes apply predictably.

Practical recipes

Iterator vs array

Replace file() on huge files with yield-based line readers to cap memory.

Password migration

On login, password_verify against old hashes; if OK and password_needs_rehash, re-save with PASSWORD_DEFAULT.

Backward incompatible changes

Notable (full list: migration55 incompatible):

  • foreach with internal array pointers and by-reference iteration—edge cases changed; regression-test code that mutates the array being iterated.
  • list() inside foreach—ordering/assignment semantics for nested lists were tightened; verify templates that unpack nested arrays.
  • GD, intl, openssl and other extensions: method signatures and error modes—consult per-function notes if you wrap them.
  • ::class as a keyword context—ensure you did not use class as a constant name without quoting in ancient code.

Deprecated

  • mysql extension—mysqli/PDO only path forward.
  • preg_replace() /e modifier—dangerous; use preg_replace_callback().

See migration55 deprecated.

Other notes

  • empty() on expressions—behavior expanded; audit empty($x->y) patterns.
  • Password hashing cost defaults evolve over PHP versions—plan periodic rehash on login.

Closing thoughts

PHP 5.5 is the “async-friendly memory + crypto hygiene” release before syntax sugar in 5.6: master generators and password_*, close mysql, then variadics and ** in 5.6 feel like a natural next step.