Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:110107
To: PHP internals <internals@lists.php.net>
Message-ID: <f9109d72-f3d3-5b12-16bb-9ec03d164cf4@ralphschindler.com>
Date: Sun, 10 May 2020 10:49:15 -0500
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0)
 Gecko/20100101 Thunderbird/68.8.0
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Subject: Proposal For Return-If / Early Return / Guard Clause Syntax
From: ralph@ralphschindler.com (Ralph Schindler)

Hi!


# Intro

I am proposing what is a near completely syntactical addition (only 
change is to language.y) to the language. The best terminology for this 
syntax is are: `return if`, "return early", or "guard clauses".

   see: https://en.wikipedia.org/wiki/Guard_(computer_science)

Over the past few years, I've seen a growing number of blog posts, 
conference talks, and even tooling (for example code complexity 
scoring), that suggest writing guard clauses is a good practice to 
utilize.  I've also seen it more prevalent in code, and even attempts at 
achieving this with Exceptions (in an HTTP context) in a framework like 
Laravel.

   see abort_if/throw_if: 
https://laravel.com/docs/7.x/helpers#method-abort-if

It is also worth mentioning that Ruby has similar features, and I 
believe they are heavily utilized:

   see: 
https://github.com/rubocop-hq/ruby-style-guide#no-nested-conditionals


# Proposal

In an effort to make it a first class feature of the language, and to 
make the control flow / guard clauses more visible when scanning code, I 
am proposing this in the syntax of adding `return if`.

The chosen syntax is:

   return if ( if_expr ) [: optional_return_expression] ;

As a contrived example:

     function divide($dividend, $divisor = null) {
         return if ($divisor === null || $divisor === 0);

         return $dividend / $divisor;
     }

There is already a little discussion around the choice of order in the 
above statement, the main take-aways and (my) perceived benefits are:

   - it keeps the intent nearest the left rail of the code (in 
normal/common-ish coding standards)

   - it treats "return if" as a meta-keyword; if must follow return for 
the statement to be a guard clause.  This also allows a person to more 
easily discern "returns" from "return ifs" more easily since there is 
not an arbitrary amount of code between them (for example if the return 
expression were after return but before if).

   - it has the quality that optional parts are towards the end

   - is also has the quality that the : return_expression; is very 
symmetrical to the way we demarcate the return type in method signatures
"): return type {" for example.

   - has the quality of promoting single-line conditional returns


# Finally

One might say this is unnecessary syntactic sugar, which is definitely 
arguable. But we do have multiple ways of achieving this.

Of course all of these things should be discussed, I think sub-votes 
(should this PR make it that far) could be considered.

The PR is located here:

   https://github.com/php/php-src/pull/5552

As mentioned, some discussion is happening there as well.


Thanks!
Ralph Schindler


PS: since implementing the ::class feature 8 years ago, the addition of 
the AST abstraction made this kind of syntactical change 
proof-of-concept so much easier, bravo!