feat: narrow ResultInterface to concrete implementation after calling isSucceeded() and isFailed()

src/Psl/Result/ResultInterface.php

@@ -53,6 +53,8 @@ public function getThrowable(): Throwable;
      * @return bool - `true` if the operation succeeded; `false` otherwise
      *
      * @psalm-mutation-free
+     *
+     * @psalm-assert-if-true Success<T> $this
      */
     public function isSucceeded(): bool;
 
@@ -64,6 +66,8 @@ public function isSucceeded(): bool;
      * @return bool - `true` if the operation failed; `false` otherwise
      *
      * @psalm-mutation-free
+     *
+     * @psalm-assert-if-true Failure<T> $this
      */
     public function isFailed(): bool;
 

tests/static-analysis/Result/result_interface.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psl\Tests\StaticAnalysis\Iter;
+
+use Exception;
+use Psl\Result\Failure;
+use Psl\Result\ResultInterface;
+use Psl\Result\Success;
+
+/**
+ * @param ResultInterface<int> $result
+ *
+ * @throws Exception
+ *
+ * @return Failure<int, Exception>
+ */
+function return_failure(ResultInterface $result): Failure
+{
+    if ($result->isFailed()) {
+        return $result;
+    }
+
+    throw new Exception();
+}
+
+/**
+ * @param ResultInterface<int> $result
+ *
+ * @throws Exception
+ *
+ * @return Success<int>
+ */
+function return_success(ResultInterface $result): Success
+{
+    if ($result->isSucceeded()) {
+        return $result;
+    }
+
+    throw new Exception();
+}