Using a callback in implode()

Question

I have a multidimensional array, e.g.:

$values = array(
    'one' => array(
        'title' => 'Title One',
        'uri'   => 'http://example.com/one',
    ),
    'two' => array(
        'title' => 'Title Two',
        'uri'   => 'http://example.com/two',
    ),
);

...and I'd like to parse through that with a closure in my implode function, à la:

$final_string = implode(' | ', function($values) {
    $return = array();

    foreach($values as $value)
        $return[] = '<a href="' . $value['uri'] . '">' . $value['title'] . '</a>';

    return $return;
});

However, this usage yields an Invalid arguments passed error. Is there syntax that I'm missing which will make this use of closures possible? I'm using PHP v5.3.16.

Answer 1

Use array_map:

$final_string = implode(' | ', array_map(function($item) {
    return '<a href="' . $item['uri'] . '">' . $item['title'] . '</a>';
}, $values));

I trust you'll properly escape the values as HTML in your real code.

---

As to why this works and your code doesn't, you were passing a function as the second argument to implode. Frankly, that makes little sense: you can join a bunch of strings together, or maybe even a bunch of functions, but you can't join a single function together. It sounds strange, especially if you word it that way.

Instead, we first want to transform all of the items in an array using a function and pass the result of that into implode. This operation is most commonly called map. Luckily, PHP provides this function as, well, array_map. After we've transformed the items in the array, we can join the results.