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An interface that declares __toString() satisfies \Stringable

Group: Object compatibility · Category: language · File: objects_implicit_stringable.php

phpdoc_advanced_psalm_stringable_object measures the PHPDoc spelling stringable-object. This file asks the native question: a parameter typed \Stringable accepts an interface that declares __toString() without extending \Stringable. Source: carthage-software/mago#2450 (1.56.0). References: - mago#2450

Analyzer results

AnalyzerVersionResultDiagnostics
phan 6.0.11Phan 6.0.11 php-ast version 1.1.3 PHP version used to run Phan: 8.5.11 Pass 
objects_implicit_stringable.php:42: Argument 1 ($value) is $value of type \Conformance\Tests\ObjectsImplicitStringable\NotStringable but \Conformance\Tests\ObjectsImplicitStringable\takesStringable() takes \Stringable defined at /Users/megurine/repo/php/php-typing-conformance/conformance/tests/objects_implicit_stringable.php:31 [PhanTypeMismatchArgument]
phpstan 2.3.5PHPStan - PHP Static Analysis Tool 2.3.5 Pass reported Lv.5+ 
objects_implicit_stringable.php:42: Parameter #1 $value of function Conformance\Tests\ObjectsImplicitStringable\takesStringable expects Stringable, Conformance\Tests\ObjectsImplicitStringable\NotStringable given. [reported-from-level=5]
With strict-rules
objects_implicit_stringable.php:42: Parameter #1 $value of function Conformance\Tests\ObjectsImplicitStringable\takesStringable expects Stringable, Conformance\Tests\ObjectsImplicitStringable\NotStringable given.
psalm 6.20.9Psalm 6.20.9@f67170ac3c3b931f5088681e21d6c8babc601c08
next: 7.0.4		 Pass 
objects_implicit_stringable.php:42: Argument 1 of Conformance\Tests\ObjectsImplicitStringable\takesStringable expects Stringable, but Conformance\Tests\ObjectsImplicitStringable\NotStringable provided [InvalidArgument]
mago 1.59.0mago 1.59.0 Pass 
objects_implicit_stringable.php:42: Possible argument type mismatch for argument #1 of `Conformance\Tests\ObjectsImplicitStringable\takesStringable`: expected `Stringable`, but possibly received `Conformance\Tests\ObjectsImplicitStringable\NotStringable`. [possibly-invalid-argument]
mir 0.91.0mir 0.91.0 Fail 
objects_implicit_stringable.php:37: InvalidArgument: Argument $value of takesStringable() expects 'Stringable', got 'Conformance\Tests\ObjectsImplicitStringable\CustomStringable' [MIR0201]
objects_implicit_stringable.php:42: InvalidArgument: Argument $value of takesStringable() expects 'Stringable', got 'Conformance\Tests\ObjectsImplicitStringable\NotStringable' [MIR0201]
Expectation diff
Line 37: Expected valid value to be accepted, got ["InvalidArgument: Argument $value of takesStringable() expects 'Stringable', got 'Conformance\\Tests\\ObjectsImplicitStringable\\CustomStringable' [MIR0201]"]
phpantom 0.11.1phpantom_lsp 0.11.1 Fail 
objects_implicit_stringable.php:37: Argument 1 ($value) expects Stringable, got Conformance\Tests\ObjectsImplicitStringable\CustomStringable [type_mismatch_argument]
objects_implicit_stringable.php:42: Argument 1 ($value) expects Stringable, got Conformance\Tests\ObjectsImplicitStringable\NotStringable [type_mismatch_argument]
Expectation diff
Line 37: Expected valid value to be accepted, got ["Argument 1 ($value) expects Stringable, got Conformance\\Tests\\ObjectsImplicitStringable\\CustomStringable [type_mismatch_argument]"]
intelephense 1.18.5intelephense 1.18.5 Pass 
objects_implicit_stringable.php:42: Expected type 'Stringable'. Found 'Conformance\Tests\ObjectsImplicitStringable\NotStringable'. [P1006]
phpactor 2026.10.07.0Phpactor 2026.10.07.0 Fail

No diagnostics reported.

Expectation diff
Line 42: Expected 1 error(s)
phpy 1.0.19490phpy 1.0.19490 Fail 
objects_implicit_stringable.php:37: Argument '1' passed to Conformance\Tests\ObjectsImplicitStringable\takesStringable() is expected to be of type Stringable, Conformance\Tests\ObjectsImplicitStringable\CustomStringable given
objects_implicit_stringable.php:42: Argument '1' passed to Conformance\Tests\ObjectsImplicitStringable\takesStringable() is expected to be of type Stringable, Conformance\Tests\ObjectsImplicitStringable\NotStringable given
Expectation diff
Line 37: Expected valid value to be accepted, got ["Argument '1' passed to Conformance\\Tests\\ObjectsImplicitStringable\\takesStringable() is expected to be of type Stringable, Conformance\\Tests\\ObjectsImplicitStringable\\CustomStringable given"]
qodana 262.11879.104PhpStorm 262.11879.104 Pass 
objects_implicit_stringable.php:42: Parameter '$value' type is not compatible with declaration [PhpParamsInspection]
noverify 0.5.5NoVerify, version 0.5.5: built on: 2025.04.22 14:36:46 OS: r-kuchinskas arm64 Commit: 4774b82f8adc53fbef38f95e97af4b953b4d1529 Fail 
objects_implicit_stringable.php:37: potentially not safe call in function Conformance\Tests\ObjectsImplicitStringable\takesStringable signature of param value [notSafeCall]
objects_implicit_stringable.php:42: potentially not safe call in function Conformance\Tests\ObjectsImplicitStringable\takesStringable signature of param value [notSafeCall]
Expectation diff
Line 37: Expected valid value to be accepted, got ["potentially not safe call in function Conformance\\Tests\\ObjectsImplicitStringable\\takesStringable signature of param value [notSafeCall]"]
steins 0.1.8steins 0.1.8 (2026-09-21 revision 76306a9) Fail

No diagnostics reported.

Expectation diff
Line 42: Expected 1 error(s)
phpstan-strict 2.3.5PHPStan - PHP Static Analysis Tool 2.3.5 Pass 
objects_implicit_stringable.php:42: Parameter #1 $value of function Conformance\Tests\ObjectsImplicitStringable\takesStringable expects Stringable, Conformance\Tests\ObjectsImplicitStringable\NotStringable given.
psalm-next 7.0.4Psalm 7.0.4@fa5b1f6e665cb743838ffd865b8fc96207f9409f Pass 
objects_implicit_stringable.php:42: Argument 1 of Conformance\Tests\ObjectsImplicitStringable\takesStringable expects Stringable, but Conformance\Tests\ObjectsImplicitStringable\NotStringable provided [InvalidArgument]

Source

<?php

declare(strict_types=1);

namespace Conformance\Tests\ObjectsImplicitStringable;

/**
 * An interface that declares `__toString()` satisfies `\Stringable`.
 *
 * `phpdoc_advanced_psalm_stringable_object` measures the PHPDoc spelling
 * `stringable-object`. This file asks the native question: a parameter typed
 * `\Stringable` accepts an interface that declares `__toString()` without
 * extending `\Stringable`.
 *
 * Source: carthage-software/mago#2450 (1.56.0).
 *
 * References:
 * - https://github.com/carthage-software/mago/pull/2450
 */

interface CustomStringable
{
    public function __toString(): string;
}

interface NotStringable
{
    public function name(): string;
}

function takesStringable(\Stringable $value): void
{
}

function fromCustom(CustomStringable $value): void
{
    takesStringable($value); // V: __toString() makes the interface Stringable
}

function fromUnrelated(NotStringable $value): void
{
    takesStringable($value); // E: NotStringable has no __toString()
}