How can I access and modify external variables within anonymous functions?

Passing External Variables to Anonymous Functions as Parameters

In the realm of programming, anonymous functions offer a convenient way to encapsulated logic without requiring formal function declarations. However, accessing external variables within such anonymous functions can pose a challenge.

Capture Variables with "use"

To access an external variable within an anonymous function, the "use" keyword can be employed. This keyword binds the external variable to the anonymous function, allowing for its manipulation and modification.

Example

Consider the following scenario:

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

Here, the "use" keyword is used to bind the external variable "$result" to the anonymous function. This allows the function to access and modify the value of "$result" within its scope.

Advantages of "use"

Using "use" to capture variables offers several advantages:

• Controlled access: It restricts the anonymous function from accessing any external variable other than those explicitly listed with "use".
• Direct modification: The bound variable can be directly modified within the anonymous function, as seen in the example above where "$result" is being appended to.

Limitations of "use"

However, it's important to note that "use" variables are bound at the time of declaration, rather than the time of invocation. This means that any changes made to the variable outside the anonymous function will not be reflected within the function.

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