Re: RFC idea: Block scoped variables with "let $x = expr"

> Intuitively, I would expect this: > > { >      let $x = new Foo; >      $x->bar(); > } > somethingElse(); > > to be equivalent to this: > > let $x = new Foo; > $x->bar(); > unset($x); > somethingElse(); If this feature freed variables when going out of scope, it would be compiled more like the following (if there were multiple lets): JavaScript doesn't have destructors, but PHP does, which makes the implementation a tiny bit more complex. ``` try {     $x = new Foo();     $otherLet = new Other();     $x->bar(); } finally {     // try/finally is useful if unset($otherLet) could throw from __destruct     try {         unset($otherLet);     } finally {         unset($x);     } } somethingElse(); ``` Actually, thinking about this again, performance is hopefully less of a concern. I could safely avoid using try/finally if this was outside of a try block, as long as this was in a function scope instead of a global scope. (All variable go out of scope for uncaught exceptions) This idea is still a work in progress. It would definitely be useful to free immediately for objects (or arrays with objects) which call __destruct when the reference count goes to 0, such as RAII patterns. My concern about adding an extra unset() is that it would add some performance overhead, discouraging using this feature, but opcache should be able to optimize the unset out when unnecessary. I touched on the reasons for avoiding try blocks earlier, but hopefully they're not needed. The global scope is less likely to be vital to performance in most cases. > - Freeing it immediately would likely require the equivalent of a try{} finally{} to handle > exceptions. >   try statements prevent opcache from optimizing a function, the last time I checked. See https://github.com/php/php-src/blob/43443857b74503246ee4ca25859b302ed0ebc078/ext/opcache/Optimizer/dfa_pass.c#L42-L49