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Subject: [PHP-DEV] [RFC] [Vote] Type Guards for Classes
Date: Thu, 16 May 2024 22:31:10 +0200 (CEST)
Message-ID: <3A6.1T4AB.9eXWvq4hof.1cHcqE@seznam.cz>
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Introduction

*************




This RFC proposes a new feature in PHP: type guards for classes (or 
interfaces). This feature aims to simplify and standardize the process of =

verifying that a variable is an instance of a specific class, enhancing co=
de
readability and reducing boilerplate code.




Motivation

*************





Currently, in PHP, to ensure that a variable is an instance of a specific =

class, developers need to use the `instanceof` operator and manually throw=
 
an exception if the check fails. This results in repetitive boilerplate co=
de
scattered throughout the codebase. A new syntax, `(ClassName) $variable`, =
is
proposed to streamline this process by performing an instanceof check and =

throwing a `TypeError` if the variable is not an instance of the specified=
 
class.




Proposal

***********





Introduce a new type guard syntax for classes:




```php

(Foo) $variable;

```




This syntax will internally perform the following operations:




1. Check if `$variable` is an instance of `Foo`.

2. If the check fails, throw a `TypeError` with a message indicating the =

expected and actual types.




Example:

Consider the following class definition:




```php

class Foo {

=C2=A0 =C2=A0// class definition

}

```




To ensure a variable is an instance of `Foo`, instead of writing:




```php

if (!$variable instanceof Foo) {

=C2=A0 =C2=A0 throw new TypeError('Expected instance of Foo, got ' . getty=
pe($
variable));

}

```




Developers can use the new type guard syntax:




```php

(Foo) $variable;

```




Backward Compatibility

***************************





This feature introduces new syntax and does not affect existing code. It i=
s 
fully backward-compatible, as it does not modify or deprecate any existing=
 
functionality.

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<html><body><div>Introduction</div><div>*************</div><div><br></div>=
<div>This RFC proposes a new feature in PHP: type guards for classes (or i=
nterfaces). This feature aims to simplify and standardize the process of v=
erifying that a variable is an instance of a specific class, enhancing cod=
e readability and reducing boilerplate code.</div><div><br></div><div>Moti=
vation</div><div>*************<br></div><div><br></div><div>Currently, in =
PHP, to ensure that a variable is an instance of a specific class, develop=
ers need to use the `instanceof` operator and manually throw an exception =
if the check fails. This results in repetitive boilerplate code scattered =
throughout the codebase. A new syntax, `(ClassName) $variable`, is propose=
d to streamline this process by performing an instanceof check and throwin=
g a `TypeError` if the variable is not an instance of the specified class.=
</div><div><br></div><div>Proposal</div><div>***********<br></div><div><br=
></div><div>Introduce a new type guard syntax for classes:</div><div><br><=
/div><div>```php</div><div>(Foo) $variable;</div><div>```</div><div><br></=
div><div>This syntax will internally perform the following operations:</di=
v><div><br></div><div>1. Check if `$variable` is an instance of `Foo`.</di=
v><div>2. If the check fails, throw a `TypeError` with a message indicatin=
g the expected and actual types.</div><div><br></div><div>Example:</div><d=
iv>Consider the following class definition:</div><div><br></div><div>```ph=
p</div><div>class Foo {</div><div>&nbsp; &nbsp;// class definition</div><d=
iv>}</div><div>```</div><div><br></div><div>To ensure a variable is an ins=
tance of `Foo`, instead of writing:</div><div><br></div><div>```php</div><=
div>if (!$variable instanceof Foo) {</div><div>&nbsp; &nbsp; throw new Typ=
eError('Expected instance of Foo, got ' . gettype($variable));</div><div>}=
</div><div>```</div><div><br></div><div>Developers can use the new type gu=
ard syntax:</div><div><br></div><div>```php</div><div>(Foo) $variable;</di=
v><div>```</div><div><br></div><div>Backward Compatibility</div><div>*****=
**********************<br></div><div><br></div><div>This feature introduce=
s new syntax and does not affect existing code. It is fully backward-compa=
tible, as it does not modify or deprecate any existing functionality.</div=
></body></html>
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