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Enum cases are objects, not backing scalar values

Group: Enums · Category: language · File: enums_case_object_vs_backing_scalar.php

References: - PHP native enums - python-typing enum member/value distinction inspiration

Analyzer results

AnalyzerVersionResultDiagnostics
phan 6.0.7Phan 6.0.7 php-ast version 1.1.3 PHP version used to run Phan: 8.5.9 Pass 
enums_case_object_vs_backing_scalar.php:25: Argument 1 ($value) is Status::Active of type \BackedEnum|\Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status|\UnitEnum but \Conformance\Tests\EnumsCaseObjectVsBackingScalar\takesString() takes string defined at /Users/megurine/repo/php/php-typing-conformance/conformance/tests/enums_case_object_vs_backing_scalar.php:20 [PhanTypeMismatchArgumentReal]
phpstan 2.2.15PHPStan - PHP Static Analysis Tool 2.2.15 Pass reported Lv.5+ 
enums_case_object_vs_backing_scalar.php:25: Parameter #1 $value of function Conformance\Tests\EnumsCaseObjectVsBackingScalar\takesString expects string, Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status::Active given. [reported-from-level=5]
With strict-rules
enums_case_object_vs_backing_scalar.php:25: Parameter #1 $value of function Conformance\Tests\EnumsCaseObjectVsBackingScalar\takesString expects string, Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status::Active given.
psalm 6.18.0Psalm 6.18.0@536dd6236b39a5115385b0307b42d6d1ad431a02
next: 7.0.0-beta22		 Pass 
enums_case_object_vs_backing_scalar.php:25: Argument 1 of Conformance\Tests\EnumsCaseObjectVsBackingScalar\takesString expects string, but enum(Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status::Active) provided [InvalidArgument]
mago 1.50.0mago 1.50.0 Pass 
enums_case_object_vs_backing_scalar.php:25: Invalid argument type for argument #1 of `Conformance\Tests\EnumsCaseObjectVsBackingScalar\takesString`: expected `string`, but found `enum(Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status::Active)`. [invalid-argument]
mir 0.78.0mir 0.78.0 Pass 
enums_case_object_vs_backing_scalar.php:25: InvalidArgument: Argument $value of takesString() expects 'string', got 'Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status' [MIR0201]
phpantom 0.10.0phpantom_lsp 0.10.0 Pass 
enums_case_object_vs_backing_scalar.php:25: Argument 1 ($value) expects string, got Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status [type_mismatch_argument]
intelephense 1.18.5intelephense 1.18.5 Pass 
enums_case_object_vs_backing_scalar.php:25: Expected type 'string'. Found 'Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status'. [P1006]
phpactor 2026.06.23.0Phpactor 2026.06.23.0 Fail

No diagnostics reported.

Expectation diff
Line 25: Expected 1 error(s)
phpy 1.0.19274phpy 1.0.19274 Pass 
enums_case_object_vs_backing_scalar.php:25: Argument '1' passed to Conformance\Tests\EnumsCaseObjectVsBackingScalar\takesString() is expected to be of type string, Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status given
qodana 262.9437.196Qodana 262.9437.196 Pass 
enums_case_object_vs_backing_scalar.php:25: Parameter 'Status::Active' type is not compatible with declaration [PhpParamsInspection]
enums_case_object_vs_backing_scalar.php:25: Parameter 'Status::Active' type is not compatible with declaration [PhpStrictTypeCheckingInspection]
noverify 0.5.5NoVerify, version 0.5.5: built on: 2025.04.22 14:36:46 OS: r-kuchinskas arm64 Commit: 4774b82f8adc53fbef38f95e97af4b953b4d1529 Pass 
enums_case_object_vs_backing_scalar.php:25: Class constant \Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status::Active does not exist [undefinedConstant]
steins 0.1.8steins 0.1.8 (2026-09-21 revision 76306a9) Pass 
enums_case_object_vs_backing_scalar.php:25: argument conformance\tests\enumscaseobjectvsbackingscalar\status::Active to takesString() cannot become string $value — proven TypeError (strict mode) [type.argument-mismatch]
phpstan-strict 2.2.15PHPStan - PHP Static Analysis Tool 2.2.15 Pass 
enums_case_object_vs_backing_scalar.php:25: Parameter #1 $value of function Conformance\Tests\EnumsCaseObjectVsBackingScalar\takesString expects string, Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status::Active given.
psalm-next 7.0.0-beta22Psalm 7.0.0-beta22@de27e5724ee5997a1e3baee4d394ca6f4e46eba0 Pass 
enums_case_object_vs_backing_scalar.php:25: enum(Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status::Active) cannot be cast to string [InvalidCast]
enums_case_object_vs_backing_scalar.php:25: Argument 1 of Conformance\Tests\EnumsCaseObjectVsBackingScalar\takesString expects string, but enum(Conformance\Tests\EnumsCaseObjectVsBackingScalar\Status::Active) provided [InvalidArgument]

Source

<?php

declare(strict_types=1);

namespace Conformance\Tests\EnumsCaseObjectVsBackingScalar;

/**
 * Enum cases are objects, not backing scalar values.
 *
 * References:
 * - PHP native enums
 * - python-typing enum member/value distinction inspiration
 */

enum Status: string
{
    case Active = 'active';
}

function takesString(string $value): void
{
}

takesString('active');
takesString(Status::Active); // E: enum case object is not accepted where string is required