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 ctype extension when PHP is compiled without ctype;
• the deepclone extension (deepclone_to_array and deepclone_from_array functions);
• the mbstring and iconv extensions;
• the uuid extension;
• the MessageFormatter class and the msgfmt_format_message functions;
• 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, IntlDateFormatter and IntlListFormatter classes, limited to the "en" locale;
• the intl_error_name, intl_get_error_code, intl_get_error_message and intl_is_failure functions;
• the idn_to_ascii and idn_to_utf8 functions;
• 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 mb_ord, mb_chr and mb_scrub functions introduced in PHP 7.2 from the mbstring extension
• the sapi_windows_vt100_support function (Windows only) introduced in PHP 7.2;
• the PHP_FLOAT_* constant introduced in PHP 7.2;
• the PHP_OS_FAMILY constant introduced in PHP 7.2;
• the is_countable function introduced in PHP 7.3;
• the array_key_first and array_key_last functions introduced in PHP 7.3;
• the hrtime function introduced in PHP 7.3;
• the JsonException class introduced in PHP 7.3;
• the normalizer_get_raw_decomposition function introduced in PHP 7.3;
• the get_mangled_object_vars, mb_str_split and password_algos functions introduced in PHP 7.4;
• the fdiv function introduced in PHP 8.0;
• the get_debug_type function introduced in PHP 8.0;
• the preg_last_error_msg function introduced in PHP 8.0;
• the str_contains function introduced in PHP 8.0;
• the str_starts_with and str_ends_with functions introduced in PHP 8.0;
• the ValueError class introduced in PHP 8.0;
• the UnhandledMatchError class introduced in PHP 8.0;
• the FILTER_VALIDATE_BOOL constant introduced in PHP 8.0;
• the get_resource_id function introduced in PHP 8.0;
• the Attribute class introduced in PHP 8.0;
• the Stringable interface introduced in PHP 8.0;
• the PhpToken class introduced in PHP 8.0 when the tokenizer extension is enabled;
• the array_is_list function introduced in PHP 8.1;
• the enum_exists function introduced in PHP 8.1;
• the MYSQLI_REFRESH_REPLICA constant introduced in PHP 8.1;
• the ReturnTypeWillChange attribute introduced in PHP 8.1;
• the CURLStringFile class introduced in PHP 8.1 (but only if PHP >= 7.4 is used);
• the CURLOPT_ISSUERCERT_BLOB constant introduced in PHP 8.1 when curl 7.47+ is used;
• the AllowDynamicProperties attribute introduced in PHP 8.2;
• the SensitiveParameter attribute introduced in PHP 8.2;
• the SensitiveParameterValue class introduced in PHP 8.2;
• the Random\Engine interface introduced in PHP 8.2;
• the Random\CryptoSafeEngine interface introduced in PHP 8.2;
• the Random\Engine\Secure class introduced in PHP 8.2 (check arokettu/random-polyfill for more engines);
• the odbc_connection_string_is_quoted function introduced in PHP 8.2;
• the odbc_connection_string_should_quote function introduced in PHP 8.2;
• the odbc_connection_string_quote function introduced in PHP 8.2;
• the ini_parse_quantity function introduced in PHP 8.2;
• the CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256 constant introduced in PHP 8.1 when curl 7.50+ is used;
• the json_validate function introduced in PHP 8.3;
• the Override attribute introduced in PHP 8.3;
• the mb_str_pad function introduced in PHP 8.3;
• the ldap_exop_sync function introduced in PHP 8.3;
• the ldap_connect_wallet function introduced in PHP 8.3;
• the stream_context_set_options function introduced in PHP 8.3;
• the str_increment and str_decrement functions introduced in PHP 8.3;
• the Date*Exception/Error classes introduced in PHP 8.3;
• the SQLite3Exception class introduced in PHP 8.3;
• the mb_ucfirst and mb_lcfirst functions introduced in PHP 8.4;
• the array_find, array_find_key, array_any and array_all functions introduced in PHP 8.4;
• the Deprecated attribute introduced in PHP 8.4;
• the mb_trim, mb_ltrim and mb_rtrim functions introduced in PHP 8.4;
• the ReflectionConstant class introduced in PHP 8.4
• the CURL_HTTP_VERSION_3 and CURL_HTTP_VERSION_3ONLY constants introduced in PHP 8.4;
• the grapheme_str_split function introduced in PHP 8.4;
• the bcceil, bcdivmod, bcfloor and bcround functions introduced in PHP 8.4;
• the PDO driver specific sub-classes introduced in PHP 8.4;
• the get_error_handler and get_exception_handler functions introduced in PHP 8.5;
• the NoDiscard attribute introduced in PHP 8.5;
• the array_first and array_last functions introduced in PHP 8.5;
• the DelayedTargetValidation attribute introduced in PHP 8.5;
• the Filter\FilterException class introduced in PHP 8.5;
• the Filter\FilterFailedException class introduced in PHP 8.5;
• the grapheme_levenshtein function introduced in PHP 8.5;
• the locale_is_right_to_left function introduced in PHP 8.5;
• the clamp function introduced in PHP 8.6;
• the ARRAY_FILTER_USE_VALUE constant introduced in PHP 8.6;
• the SortDirection enum introduced in PHP 8.6;
• the grapheme_strrev function introduced in PHP 8.6;

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.

Polyfills target the API of the latest PHP version and backport it to older ones. The goal is that code written for a recent PHP runs unchanged on the oldest supported version; it is not to reproduce the historical behavior of every intermediate version. In practice:

• New functions, classes, constants and arguments are backported; removed or legacy behavior is not. For example, the is_hex argument that mb_decode_numericentity() lost in PHP 8.0 is not accepted by the polyfill.
• A symbol is backported only when defining it carries the native effect. A constant whose sole purpose is to switch on behavior in a function that cannot be polyfilled is left undefined, so its absence stays usable for feature detection, e.g. FILTER_THROW_ON_FAILURE, which only configures filter_var(). Declarative symbols such as attributes are polyfilled even when their runtime effect needs engine support, since reflection still conveys their semantics.
• A polyfill runs only when the native symbol is missing, so it reproduces the contract of the function it shims rather than a blanket "PHP 7" or "PHP 8" behavior. Functions that always raised a ValueError on invalid input throw on every supported version (a ValueError stub is declared on PHP < 8 where needed); functions whose native contract returned false keep returning false.
• The signatures declared by the bootstrap files match the native signature of the PHP version being run, so the polyfill stays a drop-in that the engine can supersede. New arguments that cannot be implemented are accepted and ignored, e.g. the $locale argument added to the grapheme_*() functions in PHP 8.5.
• Extensions that were never bundled with PHP, such as uuid and deepclone, follow the extension's own release history rather than PHP's. Since a polyfill cannot influence extension_loaded() nor conditionally define constants, it mirrors the newest native state, including deprecations: UUID_TYPE_DCE and UUID_TYPE_NAME are defined with a Deprecated attribute on PHP 8.5+.
• When a function is provided by both an extension polyfill (Mbstring) and a version polyfill (Php74, Php83, Php84), both implementations must behave identically, because either one may end up registered depending on the PHP version and whether the extension is loaded.

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-ctype for using the ctype functions,
• symfony/polyfill-deepclone for using the deepclone_* 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-php73 for using the PHP 7.3 functions,
• symfony/polyfill-php74 for using the PHP 7.4 functions,
• symfony/polyfill-php80 for using the PHP 8.0 functions,
• symfony/polyfill-php81 for using the PHP 8.1 functions,
• symfony/polyfill-php82 for using the PHP 8.2 functions,
• symfony/polyfill-php83 for using the PHP 8.3 functions,
• symfony/polyfill-php84 for using the PHP 8.4 functions,
• symfony/polyfill-php85 for using the PHP 8.5 functions,
• symfony/polyfill-iconv for using the iconv functions,
• symfony/polyfill-intl-grapheme for using the grapheme_* functions,
• symfony/polyfill-intl-idn for using the idn_to_ascii and idn_to_utf8 functions,
• symfony/polyfill-intl-icu for using the intl functions and classes,
• symfony/polyfill-intl-messageformatter for using the intl messageformatter,
• 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.
• symfony/polyfill-uuid for using the uuid_* functions,

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.

If your project requires a minimum PHP version it is advisable to add polyfills for lower PHP versions to the replace section of your composer.json. This removes any overhead from these polyfills as they are no longer part of your project. The same can be done for polyfills for extensions that you require.

If your project requires php 7.0, and needs the mb extension, the replace section would look something like this:

{
    "replace": {
        "symfony/polyfill-php54": "*",
        "symfony/polyfill-php55": "*",
        "symfony/polyfill-php56": "*",
        "symfony/polyfill-php70": "*",
        "symfony/polyfill-mbstring": "*"
    }
}

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.