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To: Rowan Tommins <rowan.collins@gmail.com>, "internals@lists.php.net"
	<internals@lists.php.net>
Thread-Topic: [PHP-DEV] RFC idea: Block scoped variables with "let $x = expr"
Thread-Index: AQHV+ug0CGaQ9aFqj0aNq48f2k+kqahJ7oQAgAACegKAACLlgIAAL5O8
Date: Sun, 15 Mar 2020 22:57:25 +0000
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Subject: Re: [PHP-DEV] RFC idea: Block scoped variables with "let $x = expr"
From: tysonandre775@hotmail.com (tyson andre)

Hi Rowan,=0A=
=0A=
> Do you know how the equivalent code works with function-scoped variables?=
=0A=
> As far as I can see, returning from a function will successfully call mul=
tiple=0A=
> destructors even if one of them throws an exception. Could exiting block=
=0A=
> scope use that same algorithm?=0A=
=0A=
PHP literally frees all of the variables (even the ones which are definitel=
y not reference counted)=0A=
without stopping if any of them throw an exception until everything is free=
d.=0A=
`i_free_compiled_variables` is called when exiting the function scope (e.g.=
 throw/return).=0A=
(the caller also decreases reference counts to the closure/$this, extra une=
xpected arguments, etc)=0A=
=0A=
```=0A=
static zend_always_inline void i_free_compiled_variables(zend_execute_data =
*execute_data) /* {{{ */=0A=
{=0A=
	zval *cv =3D EX_VAR_NUM(0);=0A=
	int count =3D EX(func)->op_array.last_var;=0A=
	while (EXPECTED(count !=3D 0)) {=0A=
		i_zval_ptr_dtor(cv);=0A=
		cv++;=0A=
		count--;=0A=
	}=0A=
}=0A=
```=0A=
=0A=
> Having the variable become inaccessible but not actually deallocated=0A=
> seems like it would cause a lot of confusion.=0A=
=0A=
Good point about resources, I forgot about freeing being automatic.=0A=
=0A=
I'm starting to lean towards deallocating.=0A=
=0A=
If this was used within a try block or a top-level statement,=0A=
this could probably add a new opcode to free a variable that could throw=0A=
without checking for the exception,=0A=
and only the last opcode would need to throw the last exception.=0A=
(adding a new opcode to ensure deallocation of all variables without the eq=
uivalent of=0A=
a `try/finally` block for every additional `let` variable)=0A=
=0A=
For global variables, there's already the problem in the engine that `__des=
truct()`=0A=
could itself create global variables of the same/different name.=0A=
=0A=
- Tyson=