Concept of custom type hints

typehint.php

<?php

/**
 * The typehint definition requires an implementation of ::evaluate.
 * It accepts a reference to a value as an argument.
 * From here an assertion can be performed, or the value can be modified.
 *
 * The visibility of the method and whether it is static or not may be irrelevant.
 */
typehint Int
{
    function evaluate(&$value) {
        if (!is_int($value)) {
            throw new InvalidArgumentException('Expected an integer');
        }
    }
}

/**
 * A more semantically accurate implementation may take place directly inside the body
 * of the declaration.
 *
 * The variable &$value already being exposed.
 */
typehint Int
{
    if (!is_int($value)) {
        throw new InvalidArgumentException('Expected an integer');
    }
}

/**
 * Example without typehint.
 * 
 * In this example, the argument is validated in the body of the method.
 */
class A
{
    public function test($value)
    {
        if (!is_int($value)) {
            throw new InvalidArgumentException('Expected an integer');
        }
        
        // ...
    }
}

/**
 * Example with typehint.
 * 
 * In this example, the argument is validated by the type hint.
 */
class A
{
    public function test(Int $value)
    {
        // ...
    }
}