[PHP-NOTES] note 130412 added to language.variables.scope

If you're a JavaScript programmer who came to the "Variable scope" manual page trying to figure out how to do a closure in PHP:

1. What JavaScript refers to as a "closure", is in PHP just called "inheriting variables from the parent scope"
2. In PHP, the term "closure" instead refers to the class that anonymous functions are instances of.
3. Unlike in JavaScript, you don't get access to any of the variables of the parent scope (or the global scope) automatically, except for superglobals.
4. ... except for arrow functions (in PHP they start with "fn() => "), which *do* automatically inherit variables from their parent scope.
5. For anonymous functions (i.e. functions assigned to a variable), you can add a "use" clause to access specific variables from the parent scope. Here's an example:

<?php
function outer() {
    $outervar = 1;

    // Each inherited variable must be listed in the "use" clause
    $anonfn = function($param1) use ($outervar) {
        return $param1 + $outervar;
    }
    return $anonfn;
}
?>

6. Normal functions (i.e. not assigned to a variable) are globally scoped, so there is no non-global "parent scope" to inherit from.
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Manual Page -- https://php.net/manual/en/language.variables.scope.php
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