[RFC] Allow __toString() on enums

https://wiki.php.net/rfc/stringable-enums

Author: DanielEScherzer

Zend/tests/enum/__toString.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Enum with __toString() magic method - backed enum value accessible
+--FILE--
+<?php
+
+enum Foo: string {
+	case Bar = "Baz";
+
+	public function __toString() {
+		return __CLASS__ . '::' . $this->name . ' = ' . $this->value;
+	}
+}
+
+echo Foo::Bar;
+
+?>
+--EXPECT--
+Foo::Bar = Baz

Zend/tests/enum/toString/backed_enum_value.phpt

@@ -0,0 +1,29 @@
+--TEST--
+Enum with __toString() magic method - Stringable interface added
+--FILE--
+<?php
+
+enum Foo {
+	case Bar;
+
+	public function __toString() {
+		return $this->name . ' is a case of the ' . __CLASS__ . ' enum';
+	}
+}
+
+function printStringable(Stringable $s) {
+	echo $s;
+}
+
+var_dump(class_implements(Foo::class));
+printStringable(Foo::Bar);
+
+?>
+--EXPECT--
+array(2) {
+  ["UnitEnum"]=>
+  string(8) "UnitEnum"
+  ["Stringable"]=>
+  string(10) "Stringable"
+}
+Bar is a case of the Foo enum

Zend/tests/enum/toString/magic_interface.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Enum supports __toString() magic method
+--FILE--
+<?php
+
+enum Foo {
+	case Bar;
+
+	public function __toString() {
+		return $this->name . ' is a case of the ' . __CLASS__ . ' enum';
+	}
+}
+
+echo Foo::Bar;
+
+?>
+--EXPECT--
+Bar is a case of the Foo enum

Zend/tests/enum/toString/magic_method.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Enum with __toString() magic method - param validation
+--FILE--
+<?php
+
+enum Foo {
+	case Bar;
+
+	public function __toString(mixed $arg): string {
+		return '';
+	}
+}
+
+echo Foo::Bar;
+
+?>
+--EXPECTF--
+Fatal error: Method Foo::__toString() cannot take arguments in %s on line %d

Zend/tests/enum/toString/param_validation.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Enum with __toString() magic method - return validation
+--FILE--
+<?php
+
+enum Foo {
+	case Bar;
+
+	public function __toString(): int {
+		return 5;
+	}
+}
+
+echo Foo::Bar;
+
+?>
+--EXPECTF--
+Fatal error: Foo::__toString(): Return type must be string when declared in %s on line %d

Zend/tests/enum/toString/return_validation.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Enum with __toString() magic method - visibility validation
+--FILE--
+<?php
+
+enum Foo {
+	case Bar;
+
+	private function __toString(): string {
+		return '';
+	}
+}
+
+echo Foo::Bar;
+
+?>
+--EXPECTF--
+Warning: The magic method Foo::__toString() must have public visibility in %s on line %d
+
+Fatal error: Access level to Foo::__toString() must be public (as in class Stringable) in %s on line %d

Zend/tests/enum/toString/visibility_validation.phpt

@@ -80,7 +80,7 @@ static void zend_verify_enum_properties(const zend_class_entry *ce)
 
 static void zend_verify_enum_magic_methods(const zend_class_entry *ce)
 {
-	// Only __get, __call and __invoke are allowed
+	// Only __get, __call, __toString, and __invoke are allowed
 
 	ZEND_ENUM_DISALLOW_MAGIC_METHOD(constructor, "__construct");
 	ZEND_ENUM_DISALLOW_MAGIC_METHOD(destructor, "__destruct");
@@ -89,7 +89,6 @@ static void zend_verify_enum_magic_methods(const zend_class_entry *ce)
 	ZEND_ENUM_DISALLOW_MAGIC_METHOD(__set, "__set");
 	ZEND_ENUM_DISALLOW_MAGIC_METHOD(__unset, "__unset");
 	ZEND_ENUM_DISALLOW_MAGIC_METHOD(__isset, "__isset");
-	ZEND_ENUM_DISALLOW_MAGIC_METHOD(__tostring, "__toString");
 	ZEND_ENUM_DISALLOW_MAGIC_METHOD(__debugInfo, "__debugInfo");
 	ZEND_ENUM_DISALLOW_MAGIC_METHOD(__serialize, "__serialize");
 	ZEND_ENUM_DISALLOW_MAGIC_METHOD(__unserialize, "__unserialize");