Example of string lib + interface and subclasses

stringlibphp7.php

<?php


class StringLib
{
    // This should be Container not library variable..
    // But for tests is fine..
    static $lib;

    public function __construct($lib)
    {
        return $this->testChangeLib($lib);
    }

    // Method just for tests
    public static function testChangeLibStatic( $lib )
    {
        $className = $lib . get_called_class();
        if( class_exists( $className ))
        {
            static::$lib = new $className;
        }
    }

    // Method just for tests
    public function testChangeLib( $lib ) : StringLib
    {
        $className = $lib . get_called_class();
        if( class_exists( $className ))
        {
            static::$lib = new $className;
            return $this;
        }
    }


    public function __call( string $method, array $args = [])
    {
        if( method_exists(static::$lib, $method))
        {
            return call_user_func_array( array(static::$lib, $method), $args);
        }
    }

    public static function __callStatic( string $method, array $args  = [])
    {
        if( method_exists(static::$lib, $method))
        {
            return call_user_func_array(array(static::$lib, $method), $args);
        }
    }
}

interface StringInterface
{
    public function strlen( string $string) : int;
}



class PHPStringLib implements StringInterface
{
    public function strlen( string $string) : int
    {
        return strlen($string);
    }
}


class MBStringLib implements StringInterface
{
    // This should be configurable
    static $charset = 'UTF-8';

    public function strlen( string $string) : int
    {
        return mb_strlen( $string, self::$charset);
    }
}


class CustomStringLib
{
    public function strlen($string) : int
    {
        // Just another way which again uses str_ function..
        return count(str_split($string));
    }
}

$teststring = 'One two три';

$test = new StringLib( 'MB' );
echo "\n" . $test->strlen( $teststring ) . "\n";
$test->testChangeLib( 'PHP' );
echo "\n" . $test->strlen( $teststring ) . "\n";
$test->testChangeLib( 'Custom' );
echo "\n" . $test->strlen( $teststring ) . "\n";

StringLib::testChangeLibStatic('MB');
echo "\n" . StringLib::strlen( $teststring ) . "\n";
StringLib::testChangeLibStatic('PHP');
echo "\n" . StringLib::strlen( $teststring ) . "\n";
StringLib::testChangeLibStatic('Custom');
echo "\n" . StringLib::strlen( $teststring ) . "\n";