How to call global object function inside class, getting "Undefined variable" error

Question

I'm creating this simple PHP trying to cache requests on Redis with the Predis library, I instantiated my $redis object outside of the class and I need to call it from inside the class functions. However I keep getting the Undefined variable: redis message.

I have already tried calling my cache validating function both from inside and outside the class scope.

Here is the code:

<?php
require "predis/src/Autoloader.php";
Predis\Autoloader::register();

 global $redis;

 $redis = new Predis\Client();

class SimpleJsonRequest
{
    private $redisLocal;

    public function __construct() {
        global $redis;
        $this->redisLocal =& $redis;
    }

    private static function makeRequest(string $method, string $url, array $parameters = null, array $data = null)
    {
        $opts = [
            'http' => [
                'method'  => $method,
                'header'  => 'Content-type: application/json',
                'content' => $data ? json_encode($data) : null
            ]
        ];
        $url .= ($parameters ? '?' . http_build_query($parameters) : '');
        return file_get_contents($url, false, stream_context_create($opts));
    }
    public static function get(string $url, array $parameters = null)
    {
        if(validateCache('GET', $url, $parameters))
            return json_decode(self::makeRequest('GET', $url, $parameters));
    }
    public static function post(string $url, array $parameters = null, array $data)
    {
        if(validateCache('POST', $url, $parameters, $data))
            return json_decode(self::makeRequest('POST', $url, $parameters, $data));
    }
    public static function put(string $url, array $parameters = null, array $data)
    {
        if(validateCache('PUT', $url, $parameters, $data))
            return json_decode(self::makeRequest('PUT', $url, $parameters, $data));
    }   
    public static function patch(string $url, array $parameters = null, array $data)
    {
        if(validateCache('PATCH', $url, $parameters, $data))
            return json_decode(self::makeRequest('PATCH', $url, $parameters, $data));
    }
    public static function delete(string $url, array $parameters = null, array $data = null)
    {
        if(validateCache('DELETE', $url, $parameters, $data))
            return json_decode(self::makeRequest('DELETE', $url, $parameters, $data));
    }
}

function validateCache(string $method, string $url, array $parameters = null, array $data = null)
{
    if($redis->exists($method)
        && $redis->get($method, 'url') == $url 
        && json_decode($redis->get($method, 'parameters')) == $parameters
        && json_decode($redis->get($method, 'data')) == $data)
    {
        echo'request cached';
        return false;
    }
    else
    {
        $redis->hMset($method, [
                        'url' => $url,
                        'parameters' => $parameters = null ? null : json_encode($parameters),
                        'data' => $data = null ? null : json_encode($data)
                    ]);

        $redis->expire($method, 10);

        echo 'not cached';
        return true;
    }
}

$test = new SimpleJsonRequest();
print_r($redis);
echo $test->get('1');
echo $test->get('1');

I expected it to print "not cached" first followed by "request cached" but i keep getting Undefined variable error.

Answer 1

Your validateCache function is referencing $redis without first declaring it as a global variable, as you did in your SimpleJsonRequest constructor.