How to convert PHP string as name of a function and call the function

With the extra complication of adding in the value to the HTML, I can only think of the evil eval. But for the rest, just separate the function name from the parameters and create them as an array in the JSON. These can then be passed in using the Argument unpacking ... operator. I've amended the function to show how the passed in arguments could work.

In the JSON I have

["Product", 3]

which maps onto

function getItems( $prefix, $start) {

So to put this together...

function getItems( $prefix, $start) {
    $products = array();
    $products[] = (object) array('id' => '0', 'title' => $prefix.$start);
    $products[] = (object) array('id' => '1', 'title' => $prefix.($start+1));
    return $products;
}

$jsonContent = '{"myKey":["loop", "getItems", ["Product", 3], 
            "<div><h3>{$item->title}</h3></div>"]}';

$jsonObj = json_decode($jsonContent);

$options = $jsonObj->myKey;

if($options[0] == 'loop') {

    $html = [];

    foreach($options[1](...$options[2]) as $item) {
        $html[] = eval("return \"{$options[3]}\";");
    }

    echo implode('', $html);
}

which returns

<div><h3>Product3</h3></div><div><h3>Product4</h3></div>

In order to call a string as your function, you need to remove the () from your string.

$jsonContent = '{"myKey":["loop", "getItems", "<div><h3>{$item->title}</h3></div>"]}';

Then, on your foreach() loop, add them again after $options[0] like this:

 foreach( $options[1]() as $item) {
    $html[] = $options[2];
 }

Use call_user_func to call a function from a string, and as pointed out by Andreas, use separate array positions for function and argument(s)

But I wanna point out that this is UTTERLY complicated and maybe not necessary... are there any other ways you can uncomplicate it ?

EDIT:

Why do you need to pass an arg that you don't even use anyway ?

function getItems($arg) {
    $products = array();
    $products[] = (object) array('id' => '0', 'title' => 'Product1');
    $products[] = (object) array('id' => '1', 'title' => 'Product2');
    return $products;
}

$jsonContent = '{"myKey":["loop", "getItems", "Arg1,Arg2", "<div><h3>{$item->title}</h3></div>"]}';

$jsonObj = json_decode($jsonContent);

$options = $jsonObj->myKey;

if($options[0] == 'loop') {

    $html = [];

    $args = explode(',', $options[2]);

    foreach($args as $item) {
        $html[] = call_user_func ($options[1], $item);
    }

    echo implode('', $html);
}
?>````

I think this would be more workable with a couple of changes to the JSON. First, I think it would make the code more readable if options was an object rather than an array, but this same approach should still work with an array if you prefer that. Second, I think the function arguments and any object properties used in the template should be separate options to avoid use of eval().

{
    "myKey": {
        "type": "loop",
        "function": "getItems",
        "args": [
            "Arg"
        ],
        "template": "<div><h3>%s<\/h3><\/div>",
        "properties": [
            "title"
        ]
    }
}

The code for processing options after decoding the JSON:

if ($options->type == 'loop') {
    $html = [];
    foreach (($options->function)(...$options->args) as $item) {
        $html[] = vsprintf($options->template, array_map(function ($property) use ($item) {
            return $item->$property;
        }, $options->properties));
    }
    echo implode('', $html);
}

I would not recommend using this if the JSON would ever come from any external source. It seems like a good way to let people execute arbitrary code on your system, even without eval. Even if you're only using it yourself, I think it would still be prudent to at least validate the function name against a list of allowed functions.

Code for options array rather than object:

JSON:

{"myKey":["loop","getItems",["Arg"],"<div><h3>%s<\/h3><\/div>",["title"]]}

PHP:

if ($options[0] == 'loop') {
    $html = [];
    foreach (($options[1])(...$options[2]) as $item) {
        $html[] = vsprintf($options[3], array_map(function ($property) use ($item) {
            return $item->$property;
        }, $options[4]));
    }
    echo implode('', $html);
}

This is hackish and uses eval which can be dangerous on untrusted data, but for fun:

$arg = 'something';

if($options[0] == 'loop') {
    $func = rtrim($options[1], '()');

    foreach($func($arg) as $item) {
        eval("echo \"{$options[2]}\";");
    }
}

Or a slightly different approach without an argument:

if($options[0] == 'loop') {
    eval("\$items = {$options[1]};");

    foreach($items as $item) {
        eval("echo \"{$options[2]}\";");
    }
}