rfc:list_default_value

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PHP RFC: Default Value in List Syntax

Introduction

We could destruct variables from an array with list constuct, it may be nested or a simple array. But there is no guarantee that the array can fulfill all variables, it will be simple assigned with null with notice error (not good). We will need several redundant code to handle the possible cases if we want to check it and assign it with default values.

For the similar purpose we introduced Null coalesce "??" and Ternary Operator "?:" to help write clean code.

Some clever users figured out some workaround like this User contributed notes. But that is not good enough and ugly.

Proposal

Support new syntax to set default value for list elements, when there the requested index it not found in array:

list($a, $b='default') = [1];      // a = 1, b = 'default'
list($a, $b='default') = [1, 2];  // a = 1, b = 2

This could be considered as a shortcut for:

$a = $arr[0];
$b = isset($arr[1]) ? $arr[1] : 'default';

This seems not a lot of work than the new syntax. But sometimes we need to destruct nested array and there are morn than two variables, anyway list() itself is designed to avoid assign by hand for short and clean code.

All the features and examples of the proposal.

To paraphrase Zeev Suraski, explain hows the proposal brings substantial value to be considered for inclusion in one of the world's most popular programming languages.

Remember that the RFC contents should be easily reusable in the PHP Documentation.

Backward Incompatible Changes

What breaks, and what is the justification for it?

Proposed PHP Version(s)

List the proposed PHP versions that the feature will be included in. Use relative versions such as “next PHP 5.x” or “next PHP 5.x.y”.

RFC Impact

To SAPIs

Describe the impact to CLI, Development web server, embedded PHP etc.

To Existing Extensions

Will existing extensions be affected?

To Opcache

It is necessary to develop RFC's with opcache in mind, since opcache is a core extension distributed with PHP.

Please explain how you have verified your RFC's compatibility with opcache.

New Constants

Describe any new constants so they can be accurately and comprehensively explained in the PHP documentation.

php.ini Defaults

If there are any php.ini settings then list:

  • hardcoded default values
  • php.ini-development values
  • php.ini-production values

Open Issues

Make sure there are no open issues when the vote starts!

Unaffected PHP Functionality

List existing areas/features of PHP that will not be changed by the RFC.

This helps avoid any ambiguity, shows that you have thought deeply about the RFC's impact, and helps reduces mail list noise.

Future Scope

This sections details areas where the feature might be improved in future, but that are not currently proposed in this RFC.

Proposed Voting Choices

Include these so readers know where you are heading and can discuss the proposed voting options.

State whether this project requires a 2/3 or 50%+1 majority (see voting)

Patches and Tests

Links to any external patches and tests go here.

If there is no patch, make it clear who will create a patch, or whether a volunteer to help with implementation is needed.

Make it clear if the patch is intended to be the final patch, or is just a prototype.

Implementation

After the project is implemented, this section should contain

  1. the version(s) it was merged to
  2. a link to the git commit(s)
  3. a link to the PHP manual entry for the feature

References

Links to external references, discussions or RFCs

Rejected Features

Keep this updated with features that were discussed on the mail lists.

rfc/list_default_value.1447072915.txt.gz · Last modified: 2017/09/22 13:28 (external edit)