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Date: Wed, 08 Feb 2023 22:11:27 -0800
To: "php internals" <internals@lists.php.net>
Content-Type: text/plain
Subject: Re: [PHP-DEV] RFC proposal: values getter in BackedEnum
From: larry@garfieldtech.com ("Larry Garfield")

On Wed, Feb 8, 2023, at 5:30 PM, Sergii Shymko wrote:
> Hi,
>
> I'd like to propose an improvement to backed enumerations introduced in 
> PHP 8.1.
> When using enums, it's very common to get all values using the 
> following boilerplate:
> $enumValues = array_map(
>     fn (\BackedEnum $case) => $case->value,
>     ExampleEnum::cases()
> );
>
> The primary use case is when an enum is used in a "set" (array of values).
> For example, a user inputs a subset of available values.
> The input may be optional defaulting to all values if omitted.
> For example, an array option of a CLI tool:
> $inputValues = $input->getOption('enum') ?: $enumValues
>
> The secondary use case is for informational purposes.
> For example, the CLI tool may list all available values of an enum 
> option in --help.
> The list of values can also be used to produce informative error 
> messages:
> $output->writeln("Option is invalid, allowed values: " . implode(', ', 
> $enumValues))
>
> The last use case is input validation.
> Although tryFrom() can be used, having access to all values can come in 
> handy.
> For instance, you could immediately get valid and invalid enum values:
> $invalidValues = array_diff($inputValues, $enumValues);
> The implementation would be more verbose and wasteful otherwise:
> $invalidValues = array_filter($inputValues, fn ($value) => 
> !ExampleEnum::tryFrom($value));
>
> The proposal is to add the values getter to backed enums:
> interface BackedEnum extends UnitEnum
> {
>     public static values(): array;
> }
> $enumValues = ExampleEnum::values();
>
> Indeed, it's possible to implement this userland in a trait reused across enums.
> However, the implementation in C will be substantially more performant.
> For instance, the values() method call can resolve to a constant!
>
> An alternative syntax is a pseudo-constant, for example, 
> ExampleEnum::values.
> Unlike the constant, the method would be part of the interface 
> complementing cases().
> Method cases() itself is not a constant only because it returns 
> instances.
> I'm fine with either syntax leaning towards the method for consistency.
>
> Please let me know your thoughts.
> With enough support, I'd be happy to submit an RFC and implement it myself.
> Some guidance on the performance optimization aspect may be necessary though.
> I'm still missing the karma necessary to create RFCs in the wiki.
>
> Regards,
> Sergii Shymko

I would be OK with this, assuming the method approach.  (The class constant feels clunkier.)

--Larry Garfield