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Date: Sun, 10 Jan 2021 22:40:00 +0000
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Subject: Re: "TryX" idom for Enumerations
From: marandall@php.net (Mark Randall)
Message-ID: <php.internals-112839@news.php.net>

On 10/01/2021 21:27, Larry Garfield wrote:
> The "a method that begins with try is nullable, so watch out" idiom is present in C# and Rust, but to my knowledge has never existed in PHP.  That doesn't make it bad; it actually combines quite well with the null coalesce operator to allow for default values, making a valueOrDefault() method unnecessary.

I get the advantages of returning null, in particular WRT the null 
coalescing operator.

However, when I see 'try' I instictively think 'exceptions' i.e. 
try/catch when the reality is it's the opposite and it would be the 
non-try functions which throw.

But it makes sense for those to throw.

However if you will permit me a tangent...

There is an alternative, of sorts. Something I tried investigating when 
I first started looking into PHP-SRC, but lack the skill and knowledge 
to implement myself.

A shorthand try / catch of something like the form:

<tryname>(<expr, ExceptionType => ResultExpr, ...)

At which point tryFrom becomes:

$order = attempt(SortOrder::tryFrom($input), ValueError => SortOrder::Asc);

Which would be the equivilent of:

function attempt(callable $try, array $map): mixed {
   try {
     return $try();
   }
   catch ($e) {
     foreach ($map as $class => $expr) {
        if (is_subclass_of($e, $class, true)) {
           return $expr();
        }
     }

     throw $e;
   }
}

Or just allow a mixed value to be given without a mapping for catching 
Throwable.

If added as a language construct, except each expr and $try itself would 
be parsed closure at language construct level to avoid needing to fn() 
them all e.g.

$foo = attempt(fn() => SortOrder::tryFrom($input), [ ValueError => fn() 
=> null ]);

Just a thought, perhaps a cleaner solution to a wider problem. A try / 
catch combined with a match.

It avoids the need for two methods, just provide the one that throws and 
use shorthand to assign a null if it throws.

Mark Randall