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Re: [RFC][DISCUSSION] Allow default value in list() syntax

php.internals

Andreas Hennings

9 years ago

Hello list,

I found this RFC, describing a feature I wanted for a long time:
https://wiki.php.net/rfc/list_default_value
https://marc.info/?l=php-internals&m=144707619509724

(I don't know how to correctly reply to old emails that are not in my
inbox, sorry for that. I don't like mailing lists.)

I regularly want this kind of feature when unpacking a string with explode():

list($prefix, $suffix = NULL) = explode(':', $string);
if (NULL !== $suffix) {
...
}

This is for situations where a string is coming from somewhere, we
hope it has the format "aaa:bbb", but we cannot be sure.

Sometimes I use a workaround like this:

list($prefix, $suffix) = explode(':', $string . ':');
if ('' !== $suffix) {
...
}
Which works, but means a new string will be allocated in memory.

I find the list() with default values to be a decent and
understandable language feature.

-- Andreas

Andreas Hennings

9 years ago

I don't have a strong opinion about the nested list() construct which
is also part of the RFC.
I never had a situation where I wanted this.

On Thu, Aug 10, 2017 at 11:21 PM, Andreas Hennings <andreas@dqxtech.net> wrote:

Sara Golemon

9 years ago

On Thu, Aug 10, 2017 at 5:21 PM, Andreas Hennings <andreas@dqxtech.net> wrote:

> I found this RFC, describing a feature I wanted for a long time:
> https://wiki.php.net/rfc/list_default_value
> https://marc.info/?l=php-internals&m=144707619509724
>
> I regularly want this kind of feature when unpacking a string with explode():
>
> list($prefix, $suffix = NULL) = explode(':', $string);
> if (NULL !== $suffix) {
>   ...
> }
>

Agreed. This comes up for me every time I want to parse a text file
(including about 30 minutes ago, as it happens).

+1

-Sara

randomly there

9 years ago

Would isset($suffix) not suffice here? There are several things I've
thought of that would be other alternatives to changing this language
construct, but as I don't have my laptop with me, some of the testing to
confirm behavior will have to wait.

Other concerns fall around list() already being a difficult thing for
people to understand, let alone use properly. Making it look even more like
a function definition would likely exacerbate this.

-Chris


On Aug 10, 2017 16:33, "Sara Golemon" <pollita@php.net> wrote:

On Thu, Aug 10, 2017 at 5:21 PM, Andreas Hennings <andreas@dqxtech.net>
wrote:

> I found this RFC, describing a feature I wanted for a long time:
> https://wiki.php.net/rfc/list_default_value
> https://marc.info/?l=php-internals&m=144707619509724
>
> I regularly want this kind of feature when unpacking a string with

explode():

>
> list($prefix, $suffix = NULL) = explode(':', $string);
> if (NULL !== $suffix) {
>   ...
> }
>

Agreed. This comes up for me every time I want to parse a text file
(including about 30 minutes ago, as it happens).

+1

-Sara

Andreas Hennings

9 years ago

On Fri, Aug 11, 2017 at 12:01 AM, Devnuhl Unnamed <devnuhl@gmail.com> wrote:

> Would isset($suffix) not suffice here?

You mean like so?

list($prefix, $suffix) = explode(':', 'string_without_suffix');
if (!isset($suffix)) {
..
}

The isset() is too late here, because the list() will already cause an error.

> Other concerns fall around list() already being a difficult thing for people to understand

I fail to understand what is difficult about it..
And "destructuring" is a common concept in programming languages.
https://www.startpage.com/do/search?query=destructuring&cat=web&pl=chrome&language=english
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment

The following already works in Javascript:
[a, b, c, d = 'else'] = ['aa', 'bb', 'cc'];
I just tried it in my Chromium console.

Tony Marston

9 years ago

"Andreas Hennings"  wrote in message
news:CAH0Uv3HQK5wjcd_-9GynMw34H78ZTv09q9bc=yZ10JBbeT=VOA@mail.gmail.com...

>
>On Fri, Aug 11, 2017 at 12:01 AM, Devnuhl Unnamed <devnuhl@gmail.com>
>wrote:
>> Would isset($suffix) not suffice here?
>
>You mean like so?
>
>list($prefix, $suffix) = explode(':', 'string_without_suffix');
>if (!isset($suffix)) {
>  ..
>}
>
>The isset() is too late here, because the list() will already cause an
>error.
>
>
>> Other concerns fall around list() already being a difficult thing for
>> people to understand

I agree.

>I fail to understand what is difficult about it.

The point is that other people have difficulty understanding what is
supposed to be a simple feature which is now being expanded to include more
options which change its behaviour.

>And "destructuring" is a common concept in programming languages.
>https://www.startpage.com/do/search
>?query=destructuring&cat=web&pl=chrome&language=english
>https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment
>
>The following already works in Javascript:
>[a, b, c, d = 'else'] = ['aa', 'bb', 'cc'];
>I just tried it in my Chromium console.

That fact that something like this exists in another language is no reason
to add it to PHP.

--
Tony Marston

randomly there

9 years ago

When you understand something, it often can be hard to understand why
others wouldn't. I don't see why people struggle with it either, but I do
see it happen quite a lot.

I would still think that if you are going to deconstruct something in a
structured way, you should validate your data is correct beforehand. And
that would be the more ideal solution here. But if replies to a genuine
concern over things I've witnessed is going to be met with a dismissive
attitude, I'm just going to bow out entirely.

Chris

On Aug 10, 2017 5:40 PM, "Andreas Hennings" <andreas@dqxtech.net> wrote:

Andreas Treichel

9 years ago

You can merge the result with default values like this:

[$foo, $bar, $foobar] = explode(':', 'foo:bar') + [23, 42, 1337];
var_dump($foo, $bar, $foobar);

Andreas Hennings

9 years ago

This is true, I remember having done it in the past.

I still think it would be nice and feel natural to have the default
values directly built into the list construct.

It would be a bit faster, because it does not have to allocate a new
temporary array.

Whether this difference matters depends on the case.
In my own philosophy, every code that I write to be reusable, could at
some point be used in a situation where it is repeated a lot, and thus
has a performance impact. So for my taste, it does matter.

This said, I understand it not having the greatest priority.

On Fri, Aug 11, 2017 at 7:46 PM, Andreas Treichel <gmblar@gmail.com> wrote:

Björn Larsson

9 years ago

Den 2017-08-12 kl. 02:37, skrev Andreas Hennings:

> This is true, I remember having done it in the past.
>
> I still think it would be nice and feel natural to have the default
> values directly built into the list construct.
>
> It would be a bit faster, because it does not have to allocate a new
> temporary array.
>
> Whether this difference matters depends on the case.
> In my own philosophy, every code that I write to be reusable, could at
> some point be used in a situation where it is repeated a lot, and thus
> has a performance impact. So for my taste, it does matter.
>
> This said, I understand it not having the greatest priority.
>
>
>
> On Fri, Aug 11, 2017 at 7:46 PM, Andreas Treichel <gmblar@gmail.com> wrote:
>> You can merge the result with default values like this:
>>
>> [$foo, $bar, $foobar] = explode(':', 'foo:bar') + [23, 42, 1337];
>> var_dump($foo, $bar, $foobar);
>>
>>
>>
>> --
>> PHP Internals - PHP Runtime Development Mailing List
>> To unsubscribe, visit: http://www.php.net/unsub.php
>>

One could argue that:
[$foo, $bar, $foobar = 1337] = explode(':', 'foo:bar');

is more readable. I find it a small but nice addition
that doesn't clutter the language.

r//Björn

Marco Pivetta

9 years ago

> that doesn't clutter the language.

It actually does: now we have an expression-alike node that is lazy and
only evaluated when there's no default value. That's a lot of added
semantics for such an edge case feature.

Marco Pivetta

http://twitter.com/Ocramius

http://ocramius.github.com/

On Mon, Aug 14, 2017 at 11:35 AM, Björn Larsson <bjorn.x.larsson@telia.com>
wrote: