Added error support(this also fixes generic data check)

src/Error.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace TemirkhanN\Generic;
+
+class Error
+{
+    private string $message;
+    private int $code;
+    /** @var array<mixed> */
+    private array $details;
+
+    /**
+     * @param string $message
+     * @param int $code
+     * @param array<mixed> $details
+     */
+    public function __construct(string $message, int $code = 0, array $details = [])
+    {
+        $this->message = $message;
+        $this->code    = $code;
+        $this->details = $details;
+    }
+
+    public function getMessage(): string
+    {
+        return $this->message;
+    }
+
+    public function getCode(): int
+    {
+        return $this->code;
+    }
+
+    /**
+     * @return array<mixed>
+     */
+    public function getDetails(): array
+    {
+        return $this->details;
+    }
+}

src/Exception/RuntimeException.php

@@ -7,7 +7,7 @@
 /**
  * This error shall lead to direct fix in the code
  */
-class RuntimeException extends Exception
+class RuntimeException extends \RuntimeException
 {
 
 }

src/Result.php

@@ -4,13 +4,20 @@
 
 namespace TemirkhanN\Generic;
 
+use RuntimeException;
+
 /**
  * @template T
- * @implements ResultInterface<T>
+ * @template E
+ *
+ * @implements ResultInterface<T, E>
  */
 final class Result implements ResultInterface
 {
-    private string $error = '';
+    /**
+     * @var ?E
+     */
+    private $error = null;
 
     /**
      * @var T
@@ -24,9 +31,11 @@ private function __construct()
     /**
      * phpcs:disable Squiz.Commenting.FunctionComment.TypeHintMissing
      *
-     * @param T $data
+     * @template DT
      *
-     * @return static<T>
+     * @param DT $data
+     *
+     * @return static<DT, E>
      */
     public static function success($data = null): self
     {
@@ -38,16 +47,14 @@ public static function success($data = null): self
     }
 
     /**
-     * @param string $error
+     * @template Err
+     *
+     * @param Err $error
      *
-     * @return static<T>
+     * @return static<T, Err>
      */
-    public static function error(string $error): self
+    public static function error($error): self
     {
-        if ($error === '') {
-            throw new Exception\RuntimeException('Error shall contain some valid(non-empty) message');
-        }
-
         $result        = new self();
         $result->error = $error;
 
@@ -56,21 +63,22 @@ public static function error(string $error): self
 
     public function isSuccessful(): bool
     {
-        return $this->error === '';
+        return $this->error === null;
     }
 
-    public function getError(): string
+    public function getError()
     {
+        if ($this->error === null) {
+            throw new RuntimeException('This is not an error result. Consider using isSuccessful');
+        }
+
         return $this->error;
     }
 
-    /**
-     * @return T
-     */
     public function getData()
     {
         if(!$this->isSuccessful()) {
-            throw new \RuntimeException('This is an error result. It contains no data.');
+            throw new RuntimeException('This is an error result. Consider using isSuccessful.');
         }
 
         return $this->data;

src/ResultInterface.php

@@ -6,12 +6,16 @@
 
 /**
  * @template T
+ * @template E
  */
 interface ResultInterface
 {
     public function isSuccessful(): bool;
 
-    public function getError(): string;
+    /**
+     * @return E
+     */
+    public function getError();
 
     /**
      * @return T

tests/Phpstan/WishMaker.php

@@ -12,7 +12,7 @@
 class WishMaker
 {
     /**
-     * @return ResultInterface<WishPromise>
+     * @return ResultInterface<WishPromise, string>
      */
     public function pleaseAddNativeGenerics(): ResultInterface
     {

tests/ResultTest.php

@@ -25,7 +25,6 @@ public function testSuccess(): void
         $result = Result::success(['Some data']);
 
         self::assertTrue($result->isSuccessful());
-        self::assertEmpty($result->getError());
         self::assertEquals(['Some data'], $result->getData());
     }
 }