Everything

php

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

php.internals

Reeze Xia

10 years ago

Hi internals!

I'd like to open a discussion on the RFC to allow set default values for
list() assignment:  https://wiki.php.net/rfc/list_default_value.

What is your idea?

Thanks.

--
Reeze Xia
http://reeze.cn

Dan Ackroyd

10 years ago

Hi Reeze,

On 9 November 2015 at 13:35, reeze <reeze@php.net> wrote:

> Hi internals!
>
> I'd like to open a discussion on the RFC to allow set default values for
> list() assignment:  https://wiki.php.net/rfc/list_default_value.
>
> What is your idea?

I find the list construct to be quite magic already. Isn't it possible
to get the affect that you want without adding anything to the core by
doing this:

$defaults = ['default', 'default'];
$input = [1];

list($a, $b) = array_replace($defaults, $input);

I'd find that way easier to understand and explain to junior devs,
compared to having more functionality added to the 'list' magicness.

cheers
Dan

Reeze Xia

10 years ago

Hey Dan,

On 9 November 2015 at 23:24, Dan Ackroyd <danack@basereality.com> wrote:

> Hi Reeze,
>
> On 9 November 2015 at 13:35, reeze <reeze@php.net> wrote:
> > Hi internals!
> >
> > I'd like to open a discussion on the RFC to allow set default values for
> > list() assignment:  https://wiki.php.net/rfc/list_default_value.
> >
> > What is your idea?
>
> I find the list construct to be quite magic already. Isn't it possible

to get the affect that you want without adding anything to the core by

> doing this:
>
> $defaults = ['default', 'default'];
> $input = [1];
>
> list($a, $b) = array_replace($defaults, $input);
>
> I'd find that way easier to understand and explain to junior devs,
>

I saw the contrast way, it is more complex ;-). This seems like a trick.
Many feature could also be remove,
such as I refered in RFC:  Null coalesce "??" and Ternary Operator "?:"

And the trick is trick. If you want to unpack nested array.

list($a, list(list($b))) = $array

Then you might need a new trick to do that.

You know we have default for function declaration:
function func($a='default') {}; and almost all language have the feature,
it is easier to understand from my perspective.

> compared to having more functionality added to the 'list' magicness.
>
> cheers
> Dan
>

--
Reeze Xia
http://reeze.cn

Reeze Xia

10 years ago

Bump this to continue discussion of this RFC (
https://wiki.php.net/rfc/list_default_value).

In case some of you didn't follow it before. This RFC propose to allow set
default value in list() assignment：

list($a = 'default value') = $arr;


On 10 November 2015 at 11:14, reeze <reeze@php.net> wrote:

> Hey Dan,
>
> On 9 November 2015 at 23:24, Dan Ackroyd <danack@basereality.com> wrote:
>
>> Hi Reeze,
>>
>> On 9 November 2015 at 13:35, reeze <reeze@php.net> wrote:
>> > Hi internals!
>> >
>> > I'd like to open a discussion on the RFC to allow set default values for
>> > list() assignment:  https://wiki.php.net/rfc/list_default_value.
>> >
>> > What is your idea?
>>
>> I find the list construct to be quite magic already. Isn't it possible
>
> to get the affect that you want without adding anything to the core by
>> doing this:
>>
>> $defaults = ['default', 'default'];
>> $input = [1];
>>
>> list($a, $b) = array_replace($defaults, $input);
>>
>> I'd find that way easier to understand and explain to junior devs,
>>
>
> I saw the contrast way, it is more complex ;-). This seems like a trick.
> Many feature could also be remove,
> such as I refered in RFC:  Null coalesce "??" and Ternary Operator "?:"
>
> And the trick is trick. If you want to unpack nested array.
>
> list($a, list(list($b))) = $array
>
> Then you might need a new trick to do that.
>
> You know we have default for function declaration:
> function func($a='default') {}; and almost all language have the feature,
> it is easier to understand from my perspective.
>
>
>> compared to having more functionality added to the 'list' magicness.
>>
>> cheers
>> Dan
>>
>
>
>
> --
> Reeze Xia
> http://reeze.cn
>

--
Reeze Xia
http://reeze.cn

randomly there

10 years ago

On 1/21/2016 8:49 AM, reeze wrote:

> Bump this to continue discussion of this RFC (
> https://wiki.php.net/rfc/list_default_value).
>
> In case some of you didn't follow it before. This RFC propose to allow set
> default value in list() assignment：
>
> list($a = 'default value') = $arr;
>

tl;dr - List is like a contract that the array must honor.

This would seem to me a bad idea as it is already difficult enough getting
people to not think of list() as a function, but as a construct that
imports to named variables elements from an array.

You should also likely only be using list for arrays with known structures,
otherwise how do you know you're defaulting the right variable? Do you
default in front, or in back? Which values are missing from the array that
should be imported to variables and why? Should you not be populating the
array with default values?

For this to even be discussed, I feel like there would need to be a few
concrete examples of how this would be useful. If you're passing an array
to the list construct, you're telling PHP that you know how many values are
in it, and that you want them all to be filled with a value.

For example, in a dynamically generated array, the value that is missing
may be in the middle, but you can't determine where the missing value is,
only that the array is not the appropriate length.

If it's the result of a database query, the query should be returning all
values that will be populated into variables, anything missing is itself
incorrect, and building the list construct in a way to handle the data
being incorrect seems counterproductive. Instead the query should return
all the data that is expected by the construct. List is like a contract
that the array must honor.

Also, what happens when you feed a defaulted list construct bad input that
would currently result in the values being set to NULL? Would they still be
set to NULL, or would they be populated with the default value provided?

Adjusting the example from the documentation:
// list() doesn't work with strings
list($bar = 'default') = "abcde";
var_dump($bar); // NULL

or

var_dump($bar); // string(7) "default"

Sorry if this got a little long. Definitely think there needs to be some
justification behind it, though, and concrete examples of usefulness as
mentioned earlier. And generally speaking, I think treating constructs as
functions in terms of definition should be avoided.

Thanks.
Chris