What is the prevailing sentiment about extract() and compact() ? View as Markdown

Robert Landers
Software Engineer
Utrecht NL

try {
// do stuff
} catch(Throwable $exception) {
$this->logger->error("failed to do stuff", compact('exception'));
throw $exception;
}

I wonder why not just create an array with the key...

try {
   // do stuff
} catch(Throwable $exception) {
   $this->logger->error("failed to do stuff", ['exception' => $exception]));
   throw $exception;
}

It's a few more characters of course, but I would pick the readability
and simplicity over the potential typos (which the IDE should point
out) and a few key presses it saves.I

Hey Ayesh,

Yeah, this is very much a personal preference kind of thing. I choose
compact not because it is shorter to type, but because typos are a
thing if you've been around PHP for awhile... who hasn't opened a
function written 15 years ago with a misspelled variable that you want
to fix but it has been that way for 15 years, so you don't fix it.

I've also used compact inside array_maps like:

$arr = array_map(function($a) {
$name = $a['first'] . " " . $a['last'];
// more mappings
return compact('name', ...);
}, $arr);

just because it is easier to type/read than a bunch of array accesses.
Possibly faster as well, but if it is, it's by nano-seconds.

Robert Landers
Software Engineer
Utrecht NL

L.S.,

What with all the drives towards cleaner code, how do people feel
nowadays about extract() and compact() still being supported ?

Both have alternatives. The alternatives may be a little more cumbersome
to type, but also make the code more descriptive, lessens the risk of
variable name collisions (though this can be handled via the $flags in
extract), prevents surprises when a non-associative key would be
included in an array and lessens security risks when used on untrusted data

snip

I can imagine these could be candidates for deprecation ? Or limited
deprecation - only when used in the global namespace ?

For now, I'm just wondering how people feel about these functions.

Smile,
Juliette

extract() has very limited use in some kinds of template engine, which use PHP require() as a template mechanism. I don't think compact() has any uses.

I very recently was just reminded that these even exist, as i had to tell one of my developers to not use them. I think it was compact() he was trying to use. I vetoed it.

I would not mind if they were removed, but I don't know how large the BC impact would be. They'd probably need a long deprecation period, just to be safe.

--Larry Garfield

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Hi,

While I think I understand the goal behind this, I think you're missing some factors here.

Regarding use-cases for compact: the most common one I can think of from my work, is for passing multiple local variables as context to a logging function, but I'd be surprised if its not also used to build faux hash structures too.

If your goal is to achieve an associative array (i.e a poor mans hash) of known variable names, using compact in php8+ has less risk of uncaught/unexpected errors than building it manually. Passing an undefined name (i.e. due a typo, or it just not being defined) produces a warning regardless of whether you build the array manually or pass the name(s) to compact(). Providing an array key name that doesn't match the variable name (e.g. due to a typo, or a variable being renamed) will produce no error when building the array manually, but will produce a warning with compact().

IDEs (e.g. PHPStorm/IDEA+PHP plugin) can already understand that the names passed to compact are a variable name, and make changes when a variable is renamed via the IDE. They simply cannot do the same for plain array keys.

Due to how variable scope works, the only way to re-implement compact() with the same key-typo-catching behaviour as a function in userland would be something that requires the user to pass the result of get_defined_vars() to every call.

So no, I don't think compact() should be deprecated, what I think should happen, is to promote the current warning on undefined variables, to an error, as per https://wiki.php.net/rfc/undefined_variable_error_promotion. Whether this is a foregone conclusion or not, I don't know because that RFC doesn't mention compact() specifically.

extract(), as Larry points out has historically been used by 'pure php' style template systems, in a manner that's generally "safe". Personally I'm less inclined to use this behaviour now (i.e. I'd prefer to access named & typed properties from a template than arbitrary local variable names) but I don't think that's enough of a case to remove it, because just like with compact, by nature of how variable scope works, it's very difficult/impossible to re-implement this in userland, in a way that's reusable and doesn't involve using worse constructs (e.g. eval'ing the result of a function)

I think there's possibly an argument to be made for improvements, such as changing the default mode of extract to something besides EXTR_OVERWRITE, or to have checks in place preventing the overwrite of superglobals.

Cheers

Stephen

FWIW, I use compact all the time, usually like this:

try {
// do stuff
} catch(Throwable $exception) {
$this->logger->error("failed to do stuff", compact('exception'));
throw $exception;
}

But thanks for the reminder to finish the nameof RFC, I was waiting
until after 8.3 to avoid the "trying to rush it to get into 8.3"
shenanigans that happened to another RFC around the same time. If
nameof passes, then it could make this more obvious when refactoring:

try {
// do stuff
} catch(Throwable $exception) {
$this->logger->error("failed to do stuff", compact(nameof($exception)));
}

Robert Landers
Software Engineer
Utrecht NL

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My main concern with compact and extract is the counterintuitive usage of variable names, which is also why I've personally broken production after changing a variable name. If there is another way of using compact in a way where it's used without string and with dollar sign, I won't have a problem with it. I still find compact(nameof($exception)) a little confusing personally though. I have the feeling that the wish is to have a nice syntactic sugar for compact, not sure about extract though. Extract for me is somewhat of a security concern as it will make it easy to implicitly overwrite variables from a local scope if the array being used is filled elsewhere. Someone adding an array key in another layer of code in an application can cause different behavior on a totally unrelated place when there's a variable collision, and there's no way to detect this when adding (or removing) a key from the array.

I'm all for getting rid of extract. For compact I'd like to explore alternative solutions before outright deprecating. I'm still in favor of seeing it gone in its current form though.

It would be neat to combine something like nameof into something more intuitive:

$name = "Robert";
$title = "Software Engineer";

$arr = [ $name => ..., $title => ... ];

// $arr == ['name' => 'Robert', 'title' => 'Software Engineer']

would basically mean take the name of the variable as the key and the
value as the value of the array. If we took the same semantics as
nameof, then even this would work:

$arr = [ $this->name => ..., $this->title => ... ];

// $arr == ['name' => 'Robert', 'title' => 'Software Engineer']

I'm sure there is probably a prettier way to express it, but I don't
dislike it. Then we just deprecate compact. There's already
destructuring to handle extract's case:

[ 'name' => $name, 'title' => $title ] = $arr;

Robert Landers
Software Engineer
Utrecht NL