How to Access External Variables within Anonymous Functions in PHP?

Accessing Outside Variables Using Anonymous Functions as Parameters

Problem Statement:

You have a reusable function fetch that processes database rows and allows you to perform operations on each row using an anonymous function. However, you need to concatenate a specific field from all the rows into a single variable within the anonymous function.

Solution:

To access an outside variable within an anonymous function, you can use the use keyword. This will inherit the variable from the parent scope.

Example:

$result = '';
fetch("SELECT title FROM tbl", function($r) use (&$result) {
   $result .= $r['title'];
});

How it Works:

• The use keyword is used within the anonymous function's parameter list.
• It declares that the variable $result should be inherited from the parent scope.
• By using the & symbol in the use statement, the variable is passed by reference, allowing the anonymous function to modify its value.

Note:

• use variables are early bound, meaning they use the value of the variable at the time the anonymous function is declared, not when it is called.
• This could lead to unexpected behavior if the value of the variable is modified after the anonymous function is defined.

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