How Can I Access Variables Defined Outside Callback Functions in PHP?

Accessing Variables Calculated Outside of Callback Functions

When working with callback functions, there may arise a need to utilize variables calculated outside the function's scope. The use keyword provides a solution to this challenge.

Using the 'use' Keyword

To access external variables within a callback function, the use keyword can be employed. This keyword allows you to declare the variables that you wish to inherit from the parent scope. For instance, if you have calculated an average variable ($avg) outside the callback, you can use it within the function by including the following:

$callback = function($val) use ($avg) { return $val < $avg; };

Alternative: Arrow Functions (PHP 7.4 )

Arrow functions offer an alternative approach to defining anonymous functions. They automatically capture variables from the surrounding scope, eliminating the need for the use keyword. Thus, using our previous example, you can write:

$callback = fn($val) => $val < $avg;

Integrating Callback Functions in Array Manipulation

To incorporate the callback function into an array manipulation operation, such as array_filter, you can do the following:

$filtered_array = array_filter($arr, fn($val) => $val < $avg);

This approach enables you to effectively filter elements based on a variable calculated outside the callback function, providing greater flexibility in your PHP development.

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