PHP: Developers often want scalar/basic type hints. This drop-in class enables type hints through the use of a custom error handler.

typehint.php

<?php
define('TYPEHINT_PCRE', '/^Argument (\d)+ passed to (?:(\w+)::)?(\w+)\(\) must be an instance of (\w+), (\w+) given/');

class Typehint {
    private static $Typehints = array(
        'boolean'   => 'is_bool',
        'integer'   => 'is_int',
        'float'     => 'is_float',
        'string'    => 'is_string',
        'resrouce'  => 'is_resource'
    );

    private function __Constrct() {}

    public static function initializeHandler() {
        set_error_handler('Typehint::handleTypehint');
        return TRUE;
    }

    private static function getTypehintedArgument($ThBackTrace, $ThFunction, $ThArgIndex, &$ThArgValue) {
        foreach ($ThBackTrace as $ThTrace) {
            // Match the function; Note we could do more defensive error checking.
            if (isset($ThTrace['function']) && $ThTrace['function'] == $ThFunction) {
                $ThArgValue = $ThTrace['args'][$ThArgIndex - 1];
                return TRUE;
            }
        }
        return FALSE;
    }

    public static function handleTypehint($ErrLevel, $ErrMessage) {
        if ($ErrLevel == E_RECOVERABLE_ERROR) {
            if (preg_match(TYPEHINT_PCRE, $ErrMessage, $ErrMatches)) {
                list($ErrMatch, $ThArgIndex, $ThClass, $ThFunction, $ThHint, $ThType) = $ErrMatches;

                if (isset(self::$Typehints[$ThHint])) {
                    $ThBacktrace = debug_backtrace();
                    $ThArgValue  = NULL;

                    if (self::getTypehintedArgument($ThBacktrace, $ThFunction, $ThArgIndex, $ThArgValue)) {
                        if (call_user_func(self::$Typehints[$ThHint], $ThArgValue)) {
                            return TRUE;
                        }
                    }
                }
            }
        }
        return FALSE;
    }
}

Typehint::initializeHandler();

README.md

Adapted from comment by "Daniel dot L dot Wood at Gmail dot Com" on PHP documentation site:

http://php.net/manual/en/language.oop5.typehinting.php#83442

Developers often want scalar/basic type hints. This drop-in class enables type hints through the use of a custom error handler.

Why?

1. Developers are sick of using the is_* functions to validate parameters.
2. Reduction of redundant coding for defensive coders.
3. Functions and methods become self-defining and self-documenting as to required input.

Note: You should include this code above all other code in your include headers and if you are the using set_error_handler() function you should be aware that this uses it as well. You may need to chain your set_error_handlers()

Also: Follow the typehint discussions on the PHP Internals boards.

typehint_examples.php

<?php

function teststring(string $string) { echo $string; }
function testinteger(integer $integer) { echo $integer; }
function testfloat(float $float) { echo $float; }

// This will work for class methods as well.