Symfony polyfills backporting features to lower PHP versions

v1.7.0 2018-01-31 19:39 UTC


This project backports features found in the latest PHP versions and provides compatibility layers for some extensions and functions. It is intended to be used when portability across PHP versions and extensions is desired.

Polyfills are provided for:

  • the apcu extension when the legacy apc extension is installed;
  • the mbstring and iconv extensions;
  • the Normalizer class and the grapheme_* functions;
  • the utf8_encode and utf8_decode functions from the xml extension or PHP-7.2 core;
  • the Collator, NumberFormatter, Locale and IntlDateFormatter classes;
  • the intl_error_name, intl_get_error_code, intl_get_error_message and intl_is_failure functions;
  • the hex2bin function, the CallbackFilterIterator, RecursiveCallbackFilterIterator and SessionHandlerInterface classes introduced in PHP 5.4;
  • the array_column, boolval, json_last_error_msg and hash_pbkdf2 functions introduced in PHP 5.5;
  • the password_hash and password_* related functions introduced in PHP 5.5, provided by the ircmaxell/password-compat package;
  • the hash_equals and ldap_escape functions introduced in PHP 5.6;
  • the *Error classes, the error_clear_last, preg_replace_callback_array and intdiv functions introduced in PHP 7.0;
  • the random_bytes and random_int functions introduced in PHP 7.0, provided by the paragonie/random_compat package;
  • the PHP_INT_MIN constant introduced in PHP 7.0,
  • the SessionUpdateTimestampHandlerInterface interface introduced in PHP 7.0,
  • the is_iterable function introduced in PHP 7.1;
  • a Binary utility class to be used when compatibility with mbstring.func_overload is required;
  • the spl_object_id and stream_isatty functions introduced in PHP 7.2;
  • the sapi_windows_vt100_support function (Windows only) introduced in PHP 7.2;
  • the PHP_OS_FAMILY constant introduced in PHP 7.2.

It is strongly recommended to upgrade your PHP version and/or install the missing extensions whenever possible. This polyfill should be used only when there is no better choice or when portability is a requirement.

Compatibility notes

To write portable code between PHP5 and PHP7, some care must be taken:

  • \*Error exceptions must be caught before \Exception;
  • after calling error_clear_last(), the result of $e = error_get_last() must be verified using isset($e['message'][0]) instead of null !== $e.


When using Composer to manage your dependencies, you should not require the symfony/polyfill package, but the standalone ones:

  • symfony/polyfill-apcu for using the apcu_* functions,
  • symfony/polyfill-php54 for using the PHP 5.4 functions,
  • symfony/polyfill-php55 for using the PHP 5.5 functions,
  • symfony/polyfill-php56 for using the PHP 5.6 functions,
  • symfony/polyfill-php70 for using the PHP 7.0 functions,
  • symfony/polyfill-php71 for using the PHP 7.1 functions,
  • symfony/polyfill-php72 for using the PHP 7.2 functions,
  • symfony/polyfill-iconv for using the iconv functions,
  • symfony/polyfill-intl-grapheme for using the grapheme_* functions,
  • symfony/polyfill-intl-icu for using the intl functions and classes,
  • symfony/polyfill-intl-normalizer for using the intl normalizer,
  • symfony/polyfill-mbstring for using the mbstring functions,
  • symfony/polyfill-util for using the polyfill utility helpers.

Requiring symfony/polyfill directly would prevent Composer from sharing correctly polyfills in dependency graphs. As such, it would likely install more code than required.


This package is designed for low overhead and high quality polyfilling.

It adds only a few lightweight require statements to the bootstrap process to support all polyfills. Implementations are then loaded on-demand when needed during code execution.

Polyfills are unit-tested alongside their native implementation so that feature and behavior parity can be proven and enforced in the long run.


This library is released under the MIT license.