Add support for first-class callable syntax in cast attribute

Author: zero-to-prod

README.md

@@ -289,8 +289,9 @@ The `Describe` attribute can accept these arguments.
     // Runs before 'cast'
     'pre' => [MyClass::class, 'preHook']
     // Targets the static method: `MyClass::methodName()`
-    'cast' => [MyClass::class, 'castMethod'], 
+    'cast' => [MyClass::class, 'castMethod'],
     // 'cast' => 'my_func', // alternately target a function
+    // 'cast' => MyClass::castMethod(...), // or a first-class callable (PHP 8.5+)
     // Runs after 'cast' passing the resolved value as `$value`
     'post' => [MyClass::class, 'postHook']
     'default' => 'value',
@@ -324,12 +325,15 @@ class User
     use \Zerotoprod\DataModel\DataModel;
 
     #[Describe(['cast' => [self::class, 'firstName'], 'function' => 'strtoupper'])]
+    // Or with first-class callable (PHP 8.5+):
+    // #[Describe(['cast' => self::firstName(...), 'function' => 'strtoupper'])]
     public string $first_name;
-    
+
     #[Describe(['cast' => 'uppercase'])]
     public string $last_name;
 
     #[Describe(['cast' => [self::class, 'fullName']])]
+    // Or: #[Describe(['cast' => self::fullName(...)])]
     public string $full_name;
 
     private static function firstName(mixed $value, array $context, ?\ReflectionAttribute $ReflectionAttribute, \ReflectionProperty $ReflectionProperty): string
@@ -748,6 +752,7 @@ class User
     /** @var Alias[] $Aliases */
     #[Describe([
         'cast' => [self::class, 'mapOf'],   // Use the mapOf helper method
+        // 'cast' => self::mapOf(...),       // Or use first-class callable (PHP 8.5+)
         'type' => Alias::class,             // Target type for each item
     ])]
     public array $Aliases;
@@ -791,7 +796,7 @@ class User
 
     /** @var Collection<int, Alias> $Aliases */
     #[Describe([
-        'cast' => [self::class, 'mapOf'],
+        'cast' => [self::class, 'mapOf'],   // Or: self::mapOf(...) on PHP 8.5+
         'type' => Alias::class,
     ])]
     public \Illuminate\Support\Collection $Aliases;

src/DataModel.php

@@ -8,6 +8,7 @@
 use ReflectionFunction;
 use ReflectionMethod;
 use ReflectionUnionType;
+use Closure;
 use UnitEnum;
 
 use function is_array;
@@ -44,6 +45,7 @@
  *  // Targets the static method: `MyClass::methodName()`
  *  'cast' => [MyClass::class, 'castMethod'],
  *  // 'cast' => 'my_func', // alternately target a function
+ *  // 'cast' => MyClass::castMethod(...), // or a first-class callable (PHP 8.5+)
  *  // Runs after 'cast' passing the resolved value as `$value`
  *  'post' => [MyClass::class, 'postHook']
  *  'default' => 'value',
@@ -253,7 +255,9 @@ public static function from(array|object|null|string $context = [], mixed $insta
 
             /** Property-level Cast */
             if (isset($Describe->cast)) {
-                $param_count = (new (is_array($Describe->cast) ? ReflectionMethod::class : ReflectionFunction::class)(...(array)$Describe->cast))
+                $param_count = ($Describe->cast instanceof Closure
+                    ? new ReflectionFunction($Describe->cast)
+                    : new (is_array($Describe->cast) ? ReflectionMethod::class : ReflectionFunction::class)(...(array)$Describe->cast))
                     ->getNumberOfParameters();
 
                 $self->{$property_name} = $param_count === 1

src/Describe.php

@@ -3,6 +3,7 @@
 namespace Zerotoprod\DataModel;
 
 use Attribute;
+use Closure;
 
 use function is_bool;
 use function is_string;
@@ -20,12 +21,15 @@
  *     use DataModel;
  *
  *     #[Describe(['cast' => [__CLASS__, 'firstName'], 'required' => true])]
+ *     // Or with first-class callable (PHP 8.5+):
+ *     // #[Describe(['cast' => self::firstName(...), 'required' => true])]
  *     public string $first_name;
  *
  *     #[Describe(['cast' => 'uppercase'])]
  *     public string $last_name;
  *
  *     #[Describe(['cast' => [__CLASS__, 'fullName']])]
+ *     // Or: #[Describe(['cast' => self::fullName(...)])]
  *     public string $full_name;
  *
  *
@@ -126,7 +130,7 @@ class Describe
     /**
      * @link https://github.com/zero-to-prod/data-model
      */
-    public string|array $cast;
+    public string|array|Closure $cast;
     /**
      * @see $required
      * @link https://github.com/zero-to-prod/data-model
@@ -204,12 +208,15 @@ class Describe
      *      use DataModel;
      *
      *      #[Describe(['cast' => [__CLASS__, 'firstName'], 'function' => 'strtoupper'])]
+     *      // Or with first-class callable (PHP 8.5+):
+     *      // #[Describe(['cast' => self::firstName(...), 'function' => 'strtoupper'])]
      *      public string $first_name;
      *
      *      #[Describe(['cast' => 'uppercase'])]
      *      public string $last_name;
      *
      *      #[Describe(['cast' => [__CLASS__, 'fullName'], 'required' => true])]
+     *      // Or: #[Describe(['cast' => self::fullName(...), 'required' => true])]
      *      public string $full_name;
      *
      *      private static function firstName(mixed $value, array $context, ?\ReflectionAttribute $ReflectionAttribute, \ReflectionProperty $ReflectionProperty): string
@@ -279,7 +286,7 @@ class Describe
      *  }
      *  ```
      *
-     * @param  string|array{'from'?: string, 'pre'?: string|string[], 'cast'?: string|string[], 'post'?: string|string[], 'required'?: bool, 'default'?: mixed, 'nullable'?: bool,
+     * @param  string|array{'from'?: string, 'pre'?: string|string[], 'cast'?: string|array|\Closure, 'post'?: string|string[], 'required'?: bool, 'default'?: mixed, 'nullable'?: bool,
      *                                            'ignore'?: bool, 'via'?: string}|null  $attributes
      *
      * @link https://github.com/zero-to-prod/data-model

tests/Unit/Describe/CastClosure/CastClosureTest.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Tests\Unit\Describe\CastClosure;
+
+use Closure;
+use PHPUnit\Framework\Attributes\Test;
+use ReflectionFunction;
+use Tests\TestCase;
+use Zerotoprod\DataModel\Describe;
+
+class CastClosureTest extends TestCase
+{
+    #[Test]
+    public function cast_with_single_argument_closure(): void
+    {
+        $describe = new Describe(['cast' => fn($value) => strtolower($value)]);
+
+        $this->assertInstanceOf(Closure::class, $describe->cast);
+        $this->assertEquals(1, (new ReflectionFunction($describe->cast))->getNumberOfParameters());
+        $this->assertEquals('hello', ($describe->cast)('HELLO'));
+    }
+
+    #[Test]
+    public function cast_with_four_argument_closure(): void
+    {
+        $describe = new Describe(['cast' => fn($value, $context, $attribute, $property) => strtolower($value)]);
+
+        $this->assertInstanceOf(Closure::class, $describe->cast);
+        $this->assertEquals(4, (new ReflectionFunction($describe->cast))->getNumberOfParameters());
+        $this->assertEquals('hello', ($describe->cast)('HELLO', [], null, null));
+    }
+}