Rene Korss

Anonymous functions a.k.a closures

2021-03-04T02:00:00+02:00

What are anonymous functions?

php.net description for anonymous functions:

Anonymous functions, also known as closures, allow the creation of functions which have no specified name. They are most useful as the value of callable parameters, but they have many other uses.

Let's consider case (like case on Stack Overflow) where you are looping over array of emails and send message to every email.

Code which won't work:

foreach ($emails as $email) {
    Mail::send(function ($message) {
        $message->to($email)->subject('My subject');
    });
}

For clarity: $emails is array of email addresses. Mail::send takes callable as argument and provides that callable with $message which can be used to set "to" address, subject, body etc. Their logic is unimportant for this example.

Now this callable is what is anonymous function a.k.a closure. Running this code would give you a notice:

Notice: Undefined variable: email

This is because anonymous functions have their own scope and therefore are unaware of outside variables. You have to explicitly provide anonymous functions with variables from outside scope using use language construct.

Working code:

foreach ($emails as $email) {
    Mail::send(function ($message) use ($email) {
        $message->to($email)->subject('My subject');
    });
}

Reusing anonymous functions

There may be case where you would want to reuse anonymous function. You can assign it to variable and call them by variable name.

For example, let's have an anonymous function which multiplies two numbers. Yes, it would be easier to just multiply them, but this is just for simple example :)

$multiply = function ($first, $second) {
    return $first * $second;
};

echo $multiply(2, 3); // 6
echo $multiply(2, 4); // 8

This post is based on my answer on Stack Overflow. If this helped you, consider upvoting it.

How to get second level values from multidimensional array?

2020-11-27T02:00:00+02:00

Usually developers would go for foreach to loop over every value and add them to previously created empty array.

This will result in desired output, but I will show how this can be done with one line and no looping.

Let's consider following input data:

Desired result (resulting var_dump):

array(5) {
    [0]=>
    int(1)
    [1]=>
    int(2)
    [2]=>
    int(3)
    [3]=>
    int(4)
    [4]=>
    int(5)
}

Solution: use call_user_func_array with array_merge.

$result = call_user_func_array('array_merge', $data);

And we have all values in one array.

What if arrays have matching keys?

Idea with matching keys is to only get second level arrays values (without keys).

Let's consider following input data:

$data = [
    [
        'key' => 1,
        2,
        3
    ],
    [
        'key' => 4,
        5
    ]
];

Now previous solution would give as (resulting var_dump):

// Bad
// Missing value of 1 and we have key "key"
array(4) {
    ["key"]=>
    int(4)
    [0]=>
    int(2)
    [1]=>
    int(3)
    [2]=>
    int(5)
}

To fix it, array_map and array_values will help us out.

// >= PHP7.4
$result = call_user_func_array('array_merge', array_map(fn($arr) => array_values($arr), $data));

// < PHP7.4
$result = call_user_func_array('array_merge', array_map(function($arr){return array_values($arr);}, $data));

And we still have one liner and result again is as expected:

array(5) {
    [0]=>
    int(1)
    [1]=>
    int(2)
    [2]=>
    int(3)
    [3]=>
    int(4)
    [4]=>
    int(5)
}

This post is based on my answer on Stack Overflow. If this helped you, consider upvoting it.

How to filter Google Maps markers by category?

2020-11-13T02:00:00+02:00

Let's just dig in and start by adding Google Maps to page. We need