Re: [RFC] Short Closures 2, aka auto-capture take 3

On 29/06/2022 23:31, Dan Ackroyd wrote:

Imagine some code that looks like this: // Acquire some resource e.g. an exclusive lock. $some_resource = acquire_some_resource(); $fn = fn () {

     // Free that resource
     $some_resource = null;

} // do some stuff that assumes the exclusive // lock is still active. // call the callback that we 'know' frees the resource $fn(); That's a not unreasonable piece of code to write

For that to work, it would require the variable to be captured by reference, not value. Writing to a variable captured by value, like writing to a parameter passed by value, is just writing to a local variable. In fact, the "optimisation" is in my opinion a critical part of the semantics, to avoid the opposite problem: // Acquire some resource e.g. an exclusive lock. $some_resource = acquire_some_resource(); $fn = fn () {

    // Use a variable that happens to have the same name
    // A naive implementation would see $some_resource mentioned, and capture it
    // Over-writing the local variable here makes no difference; the closure still holds the value for next time
    $some_resource = 'hello';

} // Free what we believe is the last pointer, to trigger the destructor unset($some_resource); // If $some_resource gets captured, it can only be released by destroying the closure unset($fn); Regards, -- Rowan Tommins [IMSoP]