[RFC] anti-coalescing-operator View as Markdown

On Thu, Oct 24, 2019 at 12:46 PM Stephen Reay php-lists@koalephant.com
wrote:

This sounds like an alternative approach (for solving the same basic
problem) to the nullsafe operator discussed a while back, no?

https://wiki.php.net/rfc/nullsafe_calls

At the risk of hijacking, @matthewrask asked me about ?-> a couple weeks
ago (Javascript is making this one popular), and I threw together a rough
PoC at
https://github.com/php/php-src/compare/master...sgolemon:null-coalesce which
I suspect he intends to RFC properly soon. As long as the topic is at
hand, what's the general appetite for it? Should I bother polishing the
turd?

-Sara

?-> is a great idea.

The problem is this only works for method chaining, not for function
argument nesting.
So we might want something else in addition to that.

foo(bar(baz() ???) ???);

-- Andreas

At the risk of hijacking, @matthewrask asked me about ?-> a couple weeks
ago (Javascript is making this one popular), and I threw together a rough
PoC at
https://github.com/php/php-src/compare/master...sgolemon:null-coalesce
which
I suspect he intends to RFC properly soon. As long as the topic is at
hand, what's the general appetite for it? Should I bother polishing the
turd?

It would be the best Christmas present ever.

Well. Almost.

Peter

Hi Ken

I totally agree with Andreas especially:

One purpose of the operator should be that you don't have to repeat

the variable. Here you do, e.g. $_SERVER['fname']

But if this operator provide some way not to repeat the variable it will
make sense. For example:

$_SERVER['fname'] !?? $user->setName($$)

But I think this functionality should be of something like pipeline
operator:

// send tmp variable to the next expression unconditionally
$ret = $_SERVER['fname'] |> $user->setName($$);
// send tmp variable to the next expression only when $_SERVER['fname'] is
set.
$ret = $_SERVER['fname'] ?|> $user->setName($$);

Also the syntax like above will be consistent with the proposed
safe-navigation operators.

Cheers

On Fri, Oct 25, 2019 at 3:29 AM Andreas Hennings andreas@dqxtech.net
wrote:

On Thu, Oct 24, 2019 at 1:33 PM Dan Ackroyd Danack@basereality.com
wrote:

Since PHP 7.0 brought forward the Null Coalescing Operator (??),
writing
more succinct code for how to handle null values has been a blessing.
But,
what about the inverse when you want to do something when a value is
not
null?

Hi Ken,

It may help to give a real world example, rather than a metasyntactic
one, as I can't immediately see how this would be useful.

People have been expressing a concern over 'symbol soup' for similar
ideas. The null colalesce scenario happens frequently enough, that it
seemed to overcome the hurdle needed for acceptance. Again, giving a
real world example of what you currently need to do frequently might
help other people understand the need.

cheers
Dan

Hi Dan,

After some thought, and searching through my existing code bases, I
believe
I've come up with a decent code example to help demonstrate the
usefulness
of the proposed anti-coalescing-operator:

Without !??:
<?php

class ExampleController
{
/**
* PATCH a User object.
*/
public function saveAction(int $userId)
{
$user = $this->getUser($userId);

    if (isset($_SERVER['fname']) {
        $user->setName($_SERVER['fname']);
    }

    if (isset($_SERVER['lname']) {
        $user->setName($_SERVER['lname']);
    }

    if (isset($_SERVER['mname']) {
        $user->setName($_SERVER['mname']);
    }

    if (isset($_SERVER['phone']) {
        $user->setName($_SERVER['phone']);
    }

    if (isset($_SERVER['email']) {
        $user->setName($_SERVER['email']);
    }

    $this-saveUser($user);
}

}

With !??:
<?php

class ExampleController
{
/**
* PATCH a User object.
*/
public function saveAction(int $userId)
{
$user = $this->getUser($userId);

    $_SERVER['fname'] !?? $user->setName($_SERVER['fname']);
    $_SERVER['lname'] !?? $user->setName($_SERVER['lname']);
    $_SERVER['mname'] !?? $user->setName($_SERVER['mname']);
    $_SERVER['phone'] !?? $user->setName($_SERVER['phone']);
    $_SERVER['email'] !?? $user->setName($_SERVER['email']);

    $this-saveUser($user);
}

}
Thank you,
Ken Stanley

Not convinced.

1. Most of the perceived brevity is from omitting line breaks and
   curly brackets, which is a bit misleading imo.

2. It is not the intended use of these kinds of operators (ternary or
   null coalesce). Normally you would use them to produce a value, here
   you use them for control flow only.

3. One purpose of the operator should be that you don't have to repeat
   the variable. Here you do, e.g. $_SERVER['fname']

If you would simply omit the line breaks in the first version, you
would get this:

if (isset($_SERVER['fname'])) $user->setName($_SERVER['fname']);
if (isset($_SERVER['lname'])) $user->setName($_SERVER['lname']);
if (isset($_SERVER['mname'])) $user->setName($_SERVER['mname']);
if (isset($_SERVER['phone'])) $user->setName($_SERVER['phone']);
if (isset($_SERVER['email'])) $user->setName($_SERVER['email']);

Instead of "abusing" your new operator, you could simply "abuse" the
old ternary ?: instead:

!isset($_SERVER['fname']) ?: $user->setName($_SERVER['fname']);
!isset($_SERVER['lname']) ?: $user->setName($_SERVER['lname']);
!isset($_SERVER['mname']) ?: $user->setName($_SERVER['mname']);
!isset($_SERVER['phone']) ?: $user->setName($_SERVER['phone']);
!isset($_SERVER['email']) ?: $user->setName($_SERVER['email']);

One way to not repeat the variable would be to introduce a temporary
local variable, like so:

if (NULL !== $fname = $_SERVER['fname'] ?? NULL)

$user->setName($fname);

This gets more useful if the variable expression is something longer.

A new language feature for this purpose could have an anatomy like this:
https://3v4l.org/TjuuO or
https://3v4l.org/U6arm

and the short syntax would be like so:

$product = ($x ??! NULL) * ($y ??! NULL);

or the NULL can be omitted:

$product = ($x ??!) * ($y ??!);

So, the operator would break out of the current expression context,
and produce a value one level up, a bit like a try/throw/catch would,
or like a break in switch.

This is just a basic idea, it still leaves a lot of questions open.
If the expression context is multiple levels deep, how many of these
levels are we breaking?

I am not suggesting this is a good idea, but I think it is an
improvement to the original proposal.

-- Andreas

On Thu, Oct 24, 2019 at 4:29 PM Andreas Hennings andreas@dqxtech.net
wrote:

On Thu, Oct 24, 2019 at 1:33 PM Dan Ackroyd Danack@basereality.com
wrote:

Since PHP 7.0 brought forward the Null Coalescing Operator (??),
writing
more succinct code for how to handle null values has been a blessing.
But,
what about the inverse when you want to do something when a value is
not
null?

Hi Ken,

It may help to give a real world example, rather than a metasyntactic
one, as I can't immediately see how this would be useful.

People have been expressing a concern over 'symbol soup' for similar
ideas. The null colalesce scenario happens frequently enough, that it
seemed to overcome the hurdle needed for acceptance. Again, giving a
real world example of what you currently need to do frequently might
help other people understand the need.

cheers
Dan

Hi Dan,

After some thought, and searching through my existing code bases, I
believe
I've come up with a decent code example to help demonstrate the
usefulness
of the proposed anti-coalescing-operator:

Without !??:
<?php

class ExampleController
{
/**
* PATCH a User object.
*/
public function saveAction(int $userId)
{
$user = $this->getUser($userId);

    if (isset($_SERVER['fname']) {
        $user->setName($_SERVER['fname']);
    }

    if (isset($_SERVER['lname']) {
        $user->setName($_SERVER['lname']);
    }

    if (isset($_SERVER['mname']) {
        $user->setName($_SERVER['mname']);
    }

    if (isset($_SERVER['phone']) {
        $user->setName($_SERVER['phone']);
    }

    if (isset($_SERVER['email']) {
        $user->setName($_SERVER['email']);
    }

    $this-saveUser($user);
}

}

With !??:
<?php

class ExampleController
{
/**
* PATCH a User object.
*/
public function saveAction(int $userId)
{
$user = $this->getUser($userId);

    $_SERVER['fname'] !?? $user->setName($_SERVER['fname']);
    $_SERVER['lname'] !?? $user->setName($_SERVER['lname']);
    $_SERVER['mname'] !?? $user->setName($_SERVER['mname']);
    $_SERVER['phone'] !?? $user->setName($_SERVER['phone']);
    $_SERVER['email'] !?? $user->setName($_SERVER['email']);

    $this-saveUser($user);
}

}
Thank you,
Ken Stanley

Not convinced.

1. Most of the perceived brevity is from omitting line breaks and
   curly brackets, which is a bit misleading imo.

This argument can be made about ?? And ?:, which have already passed muster
and creates a precedent. Additionally, this is meant to compliment the
existing ?? by adding a negation counterpart (similar to how == has !== and

has <).

I’m curious to what you find misleading about it? Its meant to literally be
the not-null coalescing operator.

2. It is not the intended use of these kinds of operators (ternary or
   null coalesce). Normally you would use them to produce a value, here
   you use them for control flow only.

Here is another example, not using them for flow control:

<?php

class Foo
{
/**
* @return User|null
*/
private $user;

/**
 * @return string|null
 */
public function getName(): ?string
{
    return $this->user !?? $this->user->getName();
}

}

compared to:
<?php

class Foo
{
/**
* @return User|null
*/
private $user;

/**
 * @return string|null
 */
public function getName(): ?string
{
    // or $this->user instanceof User
    return $this->user !== null ? $this->user->getName() : null;
}

}

3. One purpose of the operator should be that you don't have to repeat
   the variable. Here you do, e.g. $_SERVER['fname']

I'm not sure how that's necessarily a bad thing. Would you elaborate? Is it
simply a matter of writing the same characters twice? How is that different
than:

if (isset($_SERVER['fname'])) {
$user->setName($_SERVER['fname']);
}

If you would simply omit the line breaks in the first version, you
would get this:

if (isset($_SERVER['fname'])) $user->setName($_SERVER['fname']);
if (isset($_SERVER['lname'])) $user->setName($_SERVER['lname']);
if (isset($_SERVER['mname'])) $user->setName($_SERVER['mname']);
if (isset($_SERVER['phone'])) $user->setName($_SERVER['phone']);
if (isset($_SERVER['email'])) $user->setName($_SERVER['email']);

Ugh! I just noticed that I mistakenly did not update the method names for
each line, so I can see how this might look like flow control. Those
methods should be setFirstName, setLastName, setMiddleName, setPhone, and
setEmail respectively. My apologies.

Instead of "abusing" your new operator, you could simply "abuse" the
old ternary ?: instead:

!isset($_SERVER['fname']) ?: $user->setName($_SERVER['fname']);
!isset($_SERVER['lname']) ?: $user->setName($_SERVER['lname']);
!isset($_SERVER['mname']) ?: $user->setName($_SERVER['mname']);
!isset($_SERVER['phone']) ?: $user->setName($_SERVER['phone']);
!isset($_SERVER['email']) ?: $user->setName($_SERVER['email']);

Re; #1 and #2 here: the same argument can be made for both ?? and ?:, which
again, has already passed muster and set precedent.

One way to not repeat the variable would be to introduce a temporary
local variable, like so:

if (NULL !== $fname = $_SERVER['fname'] ?? NULL)

$user->setName($fname);

The entire point of !?? would be to keep things terse and simple in nature.
Does it fit every possible use case? No. But neither do ?? and ?:. And,
like ?? and ?:, no one is required to use it if they feel being more
verbose makes sense for their needs.

This gets more useful if the variable expression is something longer.

A new language feature for this purpose could have an anatomy like this:
https://3v4l.org/TjuuO or
https://3v4l.org/U6arm

and the short syntax would be like so:

$product = ($x ??! NULL) * ($y ??! NULL);

or the NULL can be omitted:

$product = ($x ??!) * ($y ??!);

Not sure if the ??! was on purpose as an alternative to !??, but given how
other operators put the negation operator first, I feel we should maintain
the common standard.

So, the operator would break out of the current expression context,
and produce a value one level up, a bit like a try/throw/catch would,
or like a break in switch.

Isn't this the same as the aforementioned null-safe operator [
https://wiki.php.net/rfc/nullsafe_calls]?

This is just a basic idea, it still leaves a lot of questions open.
If the expression context is multiple levels deep, how many of these
levels are we breaking?

I am not suggesting this is a good idea, but I think it is an
improvement to the original proposal.

-- Andreas

Thank you for the great feedback!

Hi Bruce

If I understand correctly.

$_SERVER['fname'] !?? $user->setName($_SERVER['fname']);

Will return the result of $user->setName($_SERVER['fname']) if
$_SERVER['fname'] is set or null if not set. While:

isset($_SERVER['fname']) && $user->setName($_SERVER['fname']);

Will return boolean.

Cheers

Hi Ken

    $_SERVER['fname'] !?? $user->setName($_SERVER['fname']);
    $_SERVER['lname'] !?? $user->setName($_SERVER['lname']);
    $_SERVER['mname'] !?? $user->setName($_SERVER['mname']);
    $_SERVER['phone'] !?? $user->setName($_SERVER['phone']);
    $_SERVER['email'] !?? $user->setName($_SERVER['email']);

What you described is already achievable with short-circuit && :

isset($_SERVER['fname']) && $user->setName($_SERVER['fname']);

Besides, it's a widely used idiom known from shell scripting.

--
Best regards,
Bruce Weirdan mailto:
weirdan@gmail.com