Re: Re: "TryX" idom for Enumerations

On Sun, Jan 10, 2021, at 4:40 PM, Mark Randall wrote: > 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. That was my initial response as well, and my main concern. To a PHP developer, the terminology seems backwards. But it's not like we haven't adopted idioms and syntax from other languages before. > 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 The main issue I see is that creating an exception is quite expensive. (Or it was the last time I bothered benchmarking it, which admittedly has been a while.) So even if you had some built in "catch and match" pseudo-function, you're still paying the cost of the exception, which is not cheap. catch-and-match is an interesting idiom, but as you say it's somewhat tangential to the question at hand. --Larry Garfield