John Davidson

Message:

I have this code from a PHP course:

<?php



$ch = curl_init();



$headers = [

    "Authorization: Client-ID YOUR_ACCESS_KEY"

];



$response_headers = [];



$header_callback = function($ch, $header) use (&$response_headers) {

    

    $len = strlen($header);

    

    $parts = explode(":", $header, 2);

    

    if (count($parts) < 2) {

        

        return $len;

    }

    

    $response_headers[$parts[0]] = trim($parts[1]);

    

    return $len;

};



curl_setopt_array($ch, [

    CURLOPT_URL => "https://api.unsplash.com/photos/random",

    CURLOPT_RETURNTRANSFER => true,

    CURLOPT_HTTPHEADER => $headers,

    CURLOPT_HEADERFUNCTION => $header_callback

]);



$response = curl_exec($ch);



$status_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);



curl_close($ch);



echo $status_code, "\n";



print_r($response_headers);



echo $response, "\n";

I'm having a hard time understanding why the header_callback is written the way it is. Mostly because of the confusion provoked by the use keyword. I've been trying to understand it, but I'm not sure I did, I have a bit of a C/C++ background and I feel like it is something similar to variable capturing from lambda expressions in CPP.

But why do I need it in this case? Couldn't I just pass &$response_headers as a function parameter?

Thanks.

---

My Answer:
In PHP, function parameters are variables that are passed into a function when it is called. These parameters allow the function to accept input values that can be used within the function's code.

When we talk about "use" in PHP, we are usually referring to the "use" keyword in anonymous functions (closures). The "use" keyword allows us to access variables from the parent scope within the anonymous function.

In the code snippet you provided, it is important to understand the difference between using function parameters and the "use" keyword in anonymous functions.

Here is an example to illustrate the difference:

php
// Using function parameters
function greet($name) {
echo "Hello, $name!";
}

greet("John"); // Output: Hello, John!

// Using the "use" keyword in an anonymous function
$greet = function($name) use ($prefix) {
echo "$prefix, $name!";
};

$prefix = "Hi";
$greet("Jane"); // Output: Hi, Jane!


In the first example, the function `greet` accepts a parameter `$name` and uses it directly within the function to greet the person by name.

In the second example, we define an anonymous function `$greet` that uses the "use" keyword to access the variable `$prefix` from the parent scope. This allows us to customize the greeting with a prefix that is defined outside of the function.

In summary, function parameters are used to pass input values into a function, while the "use" keyword in anonymous functions allows us to access variables from the parent scope within the function. Both techniques are important in PHP programming and serve different purposes.