Support Explicit Backed Enum casting

[MircoBabin]

Description

The following code:

https://3v4l.org/pfXH4#v8.5.3

<?php

echo '----- Backed integer enum -----'.PHP_EOL;
enum DayOfWeekInt : int
{
    case Monday = 1;
    case Tuesday = 2;
    case Wednesday = 3;
    case Thursday = 4;
    case Friday = 5;
    case Saturday = 6;
    case Sunday = 7;
}
$var = DayOfWeekInt::Monday;

try {
    echo '--- intval($var) --'.PHP_EOL;
    echo intval($var);    
} catch (\Throwable $ex) {
    echo $ex;
}
echo PHP_EOL;

try {
    echo '--- (int) $var ---'.PHP_EOL;
    echo (int) $var;
} catch (\Throwable $ex) {
    echo $ex;
}
echo PHP_EOL;

echo PHP_EOL;
echo '----- Backed string enum -----'.PHP_EOL;
enum DayofWeekString : string
{
    case Monday = 'monday';
    case Tuesday = 'tuesday';
    case Wednesday = 'wednesday';
    case Thursday = 'thursday';
    case Friday = 'friday';
    case Saturday = 'saturday';
    case Sunday = 'sunday';
}
$var = DayofWeekString::Monday;

try {
    echo '--- strval($var) ---'.PHP_EOL;
    echo strval($var);
} catch (\Throwable $ex) {
    echo $ex;
}
echo PHP_EOL;
    
try {
    echo '--- (string) $var ---'.PHP_EOL;
    echo (string) $var;
} catch (\Throwable $ex) {
    echo $ex;
}
echo PHP_EOL;

Resulted in this output:

----- Backed integer enum -----
--- intval($var) --

Warning: Object of class DayOfWeekInt could not be converted to int in /in/pfXH4 on line 18
1
--- (int) $var ---

Warning: Object of class DayOfWeekInt could not be converted to int in /in/pfXH4 on line 26
1

----- Backed string enum -----
--- strval($var) ---
Error: Object of class DayofWeekString could not be converted to string in /in/pfXH4:48
Stack trace:
#0 {main}
--- (string) $var ---
Error: Object of class DayofWeekString could not be converted to string in /in/pfXH4:56
Stack trace:
#0 {main}

But I expected this output instead:

no warnings, no errors and a correct explicit conversion.

----- Backed integer enum -----
--- intval($var) --
1
--- (int) $var ---
1

----- Backed string enum -----
--- strval($var) ---
monday
--- (string) $var ---
monday

PHP Version

PHP 8.5.3

Operating System

No response

[LamentXU123]

Hi. IMO This should be instead a feature request. As far as I can tell, Enums are implemented as object, and:

a. PHP does not have a __toInt() magic method in its object model, so attempting to cast any object (including an enum) to an integer will result in an error.
b. Backed enums do not implicitly implement the __toString() magic method.

The correct and standard way to retrieve the scalar value of a Backed Enum is to explicitly access its read-only value property: That is:

$value = DayOfWeekInt::Monday->value; // 1

Allowing Enums to be magically cast to scalar types would rather to be a feature request (a relatively big one) than a bug fix.

[MircoBabin]

@LamentXU123

Note: This is about backed enums which have a type int or string type.

As far as I can tell, Enums are implemented as object, and:
a. PHP does not have a __toInt() magic method in its object model, so attempting to cast any object (including an enum) to an integer will result in an error.
b. Backed enums do not implicitly implement the __toString() magic method.

That backed enums are implemented by regular objects is an implementation detail. It may hinder solving this issue, but it can never be the reason for not fixing this. Backed enums are a language construct, so Userland restrictions do not apply.

I'm not asking for a __toInt() / __toString() implementation. I'm stating an explicit cast must succeed. And that it is a bug that this does currently not work.

The correct and standard way to retrieve the scalar value of a Backed Enum is to explicitly access its read-only value property.

That is one way. Explicit casting must be the other way.

Allowing Enums to be magically cast to scalar types would rather to be a feature request (a relatively big one) than a bug fix.

I'm not asking for magically casting. I'm stating EXPLICIT casting must work out of the box.

[LamentXU123]

That is one way. Explicit casting must be the other way.

I do not have any strong opinions on this statement itself. I am just stating that by definition this should be a feature request instead of a bug fix request. A bug is something that should work per documentation but somehow it doesn't. This also determines which branch should the possible fix be merged.

Per doc for enums, "All other cast types will result in an error." so (int)$enum should fail. We do not have a scalar cast rule for enums, no matter it is backed enums or what.

Now, marking this as a feature request doesn't mean anyone won't take care of this anymore. We just need to go through a RFC process to ask the majority of the community if the feature justifies the BC break and could be useful.

We might need to hear from @Girgias about this :)

[MircoBabin]

Now, marking this as a feature request doesn't mean anyone won't take care of this anymore. We just need to go through a RFC process to ask the majority of the community if the feature justifies the BC break and could be useful.

I don't know who you mean by "We just need to go through a RFC process"?

---

To substantiate my statement about explicit cast versus magically cast. The trim(null) shows there is already a seperation between explicitly casting and magically casting.

<?php
$var = null;

// explicit cast works
echo '--- Explicit cast ---'.PHP_EOL;
echo strval($var);
echo PHP_EOL;

// magically cast fails in the future --> Deprecated: trim(): Passing null to 
// parameter #1 ($string) of type string is deprecated
echo '--- Magically cast ---'.PHP_EOL;
echo trim($var);
echo PHP_EOL;

This very same rule must apply to Backed Enums.

<?php
enum DayOfWeekInt : int
{
    case Monday = 1;
    case Tuesday = 2;
    case Wednesday = 3;
    case Thursday = 4;
    case Friday = 5;
    case Saturday = 6;
    case Sunday = 7;
}

$var = DayOfWeekInt::Sunday;

// BUG: explicit cast must work.
// At the moment this fails, that is a bug.
echo '--- Explicit cast ---'.PHP_EOL;
echo intval($var);
echo PHP_EOL;

// OK: magically cast fails --> Argument #1 ($num1) 
// must be of type int, DayOfWeekInt given
echo '--- Magically cast ---'.PHP_EOL;
echo intdiv($var, 1);
echo PHP_EOL;

[LamentXU123]

I don't know who you mean by "We just need to go through a RFC process"?

I mean people who are interested in implementing the patch (possibly including you). see: https://wiki.php.net/rfc/howto

Also please don't compare enums to null. for null, we have a well-known rule to cast null to string. And, the "seperation": trim(null) is about coercion in internal function parameter context. That behavior had its own RFC and deprecation path. It only shows that PHP may use different conversion rules in different contexts for null.

Backed enums are a different case. For enums, the documentation is clear that: if converted to object, they stay unchanged; if converted to array, an array is produced; That's it. All other casting should returns error.

So if someone wants explicit scalar casts for backed enums, that is a request to introduce new enum-specific cast rule.

Just my 2 cents.

[MircoBabin]

I don't know who you mean by "We just need to go through a RFC process"?

I mean people who are interested in implementing the patch (possibly including you). see: https://wiki.php.net/rfc/howto

Rule me out.

Also please don't compare enums to null.

This is showcasing that there is already a difference between explicit casting and magical casting. As a Php user, there are int, string, float, null, objects, ..., Enums and Backed Enums. That is the comparison I am making; if trim() seperates explicit and magical cast/coercion, then Backed Enum should also make that same seperation.

Backed enums are a different case. For enums, the documentation is clear that: if converted to object, they stay unchanged; if converted to array, an array is produced; That's it. All other casting should returns error.

I have just been reading the enumerations RFC. It states:

"
Auto-scalar conversion
Whether or not a Backed Enum can be viewed as “close enough” to its corresponding scalar value is debatable, and of debatable value. For instance, is a string-backed enum Stringable? Should an int type check accept an int-backed enum value? Should a string-backed enum work in a print statement? What about up-converting a scalar to its corresponding enum automatically?

The optimal behavior here, if any, will likely not become apparent until enums see widespread use. We have therefore opted to omit all auto-conversion at this time. If clear and compelling use cases for auto-conversion appear in the future, later PHP versions can re-introduce such auto-conversion in a more targeted, well-informed way.
"

Explicit Backed Enum conversion casting seems a compelling use case to me. It is a language gap. But as I already stated, I'm not going to follow the RFC process.

[LamentXU123]

Explicit Backed Enum casting would be useful, but it is quite complicated because I think there are several edge cases to deal with and requires quite a lot further discussion. Anyways, your statement sounds reasonable to me at least. I may try to start a conversation under this topic and write a RFC on this feature (but I still want to hear from others on this topic first). Thank you for reporting this!