PHP RFC: "var" Deprecation

• Date: 2016-02-20
• Author: Colin O'Dell colinodell@php.net
• Status: Draft
• Discussion: http://markmail.org/message/wn3ykdwgplfctho7

var is currently a simple alias for public. Both keywords provide identical functionality. This RFC therefore proposes the deprecation of var in favor of public.

PHP 4 introduced the var keyword as the only means to declare class properties. Later on PHP 5 added the public, protected, and private keywords for declaring these properties with a certain visibility level. To quote the documentation:

“The PHP 4 method of declaring a variable with the var keyword [was] supported for compatibility reasons (as a synonym for the public keyword)”

(emphasis added)

This alias was left intact for PHP 7.

This RFC proposes that var be deprecated in PHP 7.1 and its functionality removed in PHP 8.0.

var would remain a reserved word in PHP 8.0 for potential future usage.

This will eliminate duplicate functionality in the language. Both var and public behave identically and therefore both are not technically needed (other than for backwards-compatibility).

The top 10,000 packages on Packagist were analyzed (along with their dependencies) to determine the proliferation of var in the PHP ecosystem:

Because dependencies may have already been counted as “packages using var internally”, the true utilization is somewhere between 4 and 8%.

The total number of public and var keywords were counted across every file of every package (including dependencies which may be counted multiple times):

• 94% - public (1,650,084 instances)
• 6% - var (98,745 instances)

The following packages are the “worst offenders”, making up 62% of the total number of var keywords found:

• 22% - simpletest (22,116 instances)
• 17% - phpseclib (16,648 instances)
• 14% - mpdf (14,000 instances)
• 9% - simplepie (8,745 instances)

Updating these packages would drop overall var utilization to 1.5 - 3.0%.

This survey confirms that modern PHP development has largely moved away from var. Accepting this RFC will therefore have minimal impact on the ecosystem.

var is a legacy feature from PHP 4 which has been superseded by the visibility keywords. It was kept in PHP 5+ for backwards-compatibility. Removing it would help clean up the lesser-used legacy bits of the language.

There is precedent for deprecating and eventually removing other legacy features (with modern equivalents) as part of major releases:

• PHP 4 constructors were removed in 7.0
• Alternative PHP tags were removed in 7.0
• Several other previously-deprecated features were removed in 7.0

PHP 8.0 is at least a few years away. Deprecating this now (rather than later) would provide developers with sufficient notice that their code may need to be modified to work on 8.0.

Because var is currently an alias for public, updating older code is as simple as replacing var with public everywhere it appears. A utility script has been provided with this RFC to aid with the transition.

There are no technical issues with the current implementation of var and therefore no urgency to remove it.

PHP 4 classes will no longer function as-is in PHP 8.0. Furthermore, any classes written in PHP 5.x or 7.x may also break in 8.0 if they use var. BC breaks should not be taken lightly.

This change does not introduce any new functionality for developers. Those who are not using var will see no impact. Those who do use var will need to update their code.

PHP 7.1 - 7.x: usages of var will raise a deprecation notice but otherwise work as-is.

PHP 8.0: Usages of var will throw a parse error.

An upgrade tool is provided which automatically replaces all instances of var with public.

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Reserving the var keyword will allow it to be used for new functionality in 8.0 and beyond.

As this is a language change, this RFC requires a 2/3 majority to pass.

No patch has been created yet. Assistance would be greatly appreciated.

• http://markmail.org/message/wn3ykdwgplfctho7