Chapter 10 Question

[another_noob]

I am actually still beating chapter 2 to death, but started looking ahead to see what the future chapters are all about. In chapter 10, page 349 I find this script 10.5 (aka 11.5 in my book) that uses a switch to check which format was passed through the POST. Starting on line 34 of the code, Larry uses an if/else conditional to select  the format based on what the requester submitted.

 

My question is this, why would we not use another switch statement instead of the if/else? The switch looks cleaner and makes it easier to see at a quick glance what is going on. Not that it is confusing the way the code is written, it just isn't as clean and straight forward.

 

I am just wondering if there is a reason to not use a switch in this specific case even though we are checking the value of the same variable throughout the if/else.

 

In my learning, I like to see how other programmer's were thinking when a decision was made to do it "this was, or that way".    

 

Here is the code in question:

<?php # Script 10.5 - service.php
// This script acts as a simple Web service.
// The script only reports back the data received, along with a bit of extra information.

// Check for proper usage:
if (isset($_POST['format'])) {
    
    // Switch the content type based upon the format:
    switch ($_POST['format']) {
        case 'csv':
            $type = 'text/csv';
            break;
        case 'json':
            $type = 'application/json';
            break;
        case 'xml':
            $type = 'text/xml';
            break;
        default:
            $type = 'text/plain';
            break;
    }
    
    // Create the response:
    $data = array();
    $data['timestamp'] = time();
    
    // Add back in the received data:
    foreach ($_POST as $k => $v) {
        $data[$k] = $v;
    }
    
    // Format the data accordingly:
    if ($type == 'application/json') {
        $output = json_encode($data);
        
    } elseif ($type == 'text/csv') {
    
        // Convert to a string:
        $output = '';
        foreach ($data as $v) {
            $output .= '"' . $v . '",';
        }
    
        // Chop off the final comma:
        $output = substr($output, 0, -1); 

    } elseif ($type == 'text/plain') {
        $output = print_r($data, 1);
    }

} else { // Incorrectly used!
    $type = 'text/plain';
    $output = 'This service has been incorrectly used.';
}

// Set the content-type header:
header("Content-Type: $type");
echo $output;

[HartleySan]

I think the following will shed some light on this:

http://stackoverflow.com/questions/4241768/switch-vs-if-statements

 

I would recommend reading all the answers in the thread, as they all offer some valuable insight.

[another_noob]

Thanks HartleySan for the reply. I studied that thread, but can't seem to apply it to this exact situation. Maybe I am missing something. I wrote the if/else into a switch as follows:

switch($type){
	case 'application/json':
		$output = json_encode($data);
		break;
	case 'text/csv':
		$output = '';
		foreach($data as $v){
		    $output .= '"' . $v . '",';
		}
		$output = substr($output, 0, -1);
		break;
	case 'text/plain':
		$output = print_r($data, 1);
		break;
	default:
		$type = 'text/plain';
		$output = 'This service has been incorrectly used.';
}

I haven't tested the code, this is just for example. I can't find a reason to not write it this way as opposed to an if/else conditional. Surely speed can't be the issue or the switch statement above it in the original code would be an if/else. There are as many cases in my switch as there is in the original code's switch, so the number of conditions sure can't be a reason to use if/else.

 

I am thinking that the switch in the original code could of course be easily rewritten as an if/else and function just fine. 

 

This is just an OCD thing for me now. I have to know why (in this exact case) Larry chose to do it the way he did. There must be a very specific reason.

 

Assuming my rewrite of the if/else is correct, which way would you be inclined to write this code?

 

Maybe I should go back to chapter 2 and shut up...lol.

[HartleySan]

Well, we can only hope that Larry personally chimes in if you want to know why he wrote what he did.

 

As for the thread I linked to and my own understanding of if/else vs. switch, I feel like they solve two different things.

Switch statements are used when you have a set number of simple values that you are testing against (be them strings or numbers), and if/else statements are used for handling more complex logic (e.g., $x > 3 && $x * 21 < 5,653).

 

That make sense?

[Larry]

I don't like to put logic within the cases of a switch (e.g., the foreach).

[another_noob]

Ah ha, that makes sense. I knew there had to be a very specific reason. Thanks Larry.

 

Thanks HartleySan for all your input. I appreciate all your time and input you lend to this forum.

[Larry]

Yes, my continued thanks to HartleySan for is time and input, too.