PHP RFC: Add true type

• Version: 0.1
• Date: 2022-04-7
• Author: George Peter Banyard, girgias@php.net
• Status: Draft
• Target Version: PHP 8.2
• Implementation: https://github.com/php/php-src/pull/XXXX
• First Published at: http://wiki.php.net/rfc/true-type

PHP now has support for ''null'' and ''false'' as standalone types. However, true which is the natural counter part of false does not even exist as a type.

The motivations are the same to previous RFC targeting the type system:

• Type system completeness
• Providing precise type information while satisfying LSP

Add support for using true as a type declaration, wherever type declarations are currently allowed.

class Truthy {
    public true $truthy = true;
 
    public function foo(true $v): true { /* ... */ *}
}

As it is the case currently for false a compile time error will be emitted if true and bool are present in union. For example, the following function signature:

<?php
function test(): bool|true {}
?>

Will emit the following error:

Fatal error: Duplicate type true is redundant in %s on line %d

A compile time error is also emitted when true|false is used instead of bool. The following function signature:

<?php
function test(): false|true {}
?>

will emit the following error:

Fatal error: Type contains both true and false, bool should be used instead in %s on line %d

There are many examples of functions which only return true. Example of internal functions are all the array_sort functions always return true. And examples of userland projects which can benefit of this change is Composer, which has various cases where they could use a true type. [1] [2] [3] [4]

The new true type will behave as any other type in regards to Reflection.

This RFC does not contain any backwards incompatible changes.

Next minor version, i.e. PHP 8.2.

As per the voting RFC a yes/no vote with a 2/3 majority is needed for this proposal to be accepted.

Voting started on 2022-03-12 and will end on 2022-03-26.

Accept Add true type RFC?
Real name	Yes	No
aaronjunker (aaronjunker)
alec (alec)
asgrim (asgrim)
ashnazg (ashnazg)
brzuchal (brzuchal)
crell (crell)
dams (dams)
danack (danack)
derick (derick)
dharman (dharman)
ekin (ekin)
galvao (galvao)
girgias (girgias)
kalle (kalle)
kocsismate (kocsismate)
lbarnaud (lbarnaud)
levim (levim)
lufei (lufei)
marandall (marandall)
mcmic (mcmic)
nicolasgrekas (nicolasgrekas)
ocramius (ocramius)
petk (petk)
pierrick (pierrick)
ramsey (ramsey)
reywob (reywob)
sebastian (sebastian)
seld (seld)
sergey (sergey)
theodorejb (theodorejb)
trowski (trowski)
villfa (villfa)
wyrihaximus (wyrihaximus)
Final result:	33	0
This poll has been closed.

GitHub pull request: https://github.com/php/php-src/pull/XXXX

After the project is implemented, this section should contain

• the version(s) it was merged into
• a link to the git commit(s)
• a link to the PHP manual entry for the feature