From f01efd822e25be5ffdccd01f43afb9bfbeeceb7f Mon Sep 17 00:00:00 2001
From: Dario Mirovic <dario.mirovic@scylladb.com>
Date: Fri, 8 Aug 2025 08:39:31 +0200
Subject: [PATCH] utils: add result_with_exception_ptr

Add `result_with_exception_ptr` result type.
Successful result has user specified type.
Failed result has std::exception_ptr.

This approach is simpler than `result_with_exception`. It does not require
user to pass exception types as variadic template through all the callstack.
Specific exception type can still be accessed without costly std::rethrow_exception(eptr)
by using `try_catch`, if configured so via `USE_OPTIMIZED_EXCEPTION_HANDLING`.
This means no information loss, but less verbosity when writing result types.

Refs: #24567
---
 utils/result.hh | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/utils/result.hh b/utils/result.hh
index 444a23e38e..3d0426a77f 100644
--- a/utils/result.hh
+++ b/utils/result.hh
@@ -59,4 +59,24 @@ concept ResultRebindableTo =
 template<typename T, ExceptionContainerResult R>
 using rebind_result = bo::result<T, typename R::error_type, exception_container_throw_policy>;
 
+struct result_with_exception_ptr_throw_policy : bo::policy::base {
+    template<class Impl> static constexpr void wide_value_check(Impl&& self) {
+        if (!base::_has_value(self)) {
+            std::rethrow_exception(base::_error(self));
+        }
+    }
+
+    template<class Impl> static constexpr void wide_error_check(Impl&& self) {
+        if (!base::_has_error(self)) {
+            throw bo::bad_result_access("no error");
+        }
+    }
+};
+
+template<typename T>
+using result_with_exception_ptr = bo::result<T, std::exception_ptr, result_with_exception_ptr_throw_policy>;
+
+template<typename R>
+concept ExceptionPtrResult = bo::is_basic_result<R>::value && std::same_as<typename R::error_type, std::exception_ptr>;
+
 }