add and_other and or_other to toml::result

effectively same as Rust's std::Result::and and or.

tests/test_result.cpp

@@ -409,3 +409,33 @@ BOOST_AUTO_TEST_CASE(test_or_else)
         BOOST_CHECK_EQUAL(mapped.unwrap_err(), "hogehoge");
     }
 }
+
+BOOST_AUTO_TEST_CASE(test_and_or_other)
+{
+    {
+        const toml::result<int, std::string> r1(toml::ok(42));
+        const toml::result<int, std::string> r2(toml::err<std::string>("foo"));
+
+        BOOST_CHECK_EQUAL(r1,    r1.or_other(r2));
+        BOOST_CHECK_EQUAL(r2,    r1.and_other(r2));
+        BOOST_CHECK_EQUAL(42,    r1.or_other(r2).unwrap());
+        BOOST_CHECK_EQUAL("foo", r1.and_other(r2).unwrap_err());
+    }
+    {
+        auto r1_gen = []() -> toml::result<int, std::string> {
+            return toml::ok(42);
+        };
+        auto r2_gen = []() -> toml::result<int, std::string> {
+            return toml::err<std::string>("foo");
+        };
+        const auto r3 = r1_gen();
+        const auto r4 = r2_gen();
+
+        BOOST_CHECK_EQUAL(r3, r1_gen().or_other (r2_gen()));
+        BOOST_CHECK_EQUAL(r4, r1_gen().and_other(r2_gen()));
+        BOOST_CHECK_EQUAL(42,    r1_gen().or_other (r2_gen()).unwrap());
+        BOOST_CHECK_EQUAL("foo", r1_gen().and_other(r2_gen()).unwrap_err());
+    }
+}
+
+

toml/result.hpp

@@ -592,6 +592,26 @@ struct result
         return ok(std::move(this->as_ok()));
     }
 
+    // if *this is error, returns *this. otherwise, returns other.
+    result and_other(const result& other) const&
+    {
+        return this->is_err() ? *this : other;
+    }
+    result and_other(result&& other) &&
+    {
+        return this->is_err() ? std::move(*this) : std::move(other);
+    }
+
+    // if *this is okay, returns *this. otherwise, returns other.
+    result or_other(const result& other) const&
+    {
+        return this->is_ok() ? *this : other;
+    }
+    result or_other(result&& other) &&
+    {
+        return this->is_ok() ? std::move(*this) : std::move(other);
+    }
+
     void swap(result<T, E>& other)
     {
         result<T, E> tmp(std::move(*this));
@@ -638,5 +658,22 @@ void swap(result<T, E>& lhs, result<T, E>& rhs)
     return;
 }
 
+// this might be confusing because it eagerly evaluated, while in the other
+// cases operator && and || are short-circuited.
+//
+// template<typename T, typename E>
+// inline result<T, E>
+// operator&&(const result<T, E>& lhs, const result<T, E>& rhs) noexcept
+// {
+//     return lhs.is_ok() ? rhs : lhs;
+// }
+//
+// template<typename T, typename E>
+// inline result<T, E>
+// operator||(const result<T, E>& lhs, const result<T, E>& rhs) noexcept
+// {
+//     return lhs.is_ok() ? lhs : rhs;
+// }
+
 } // toml11
 #endif// TOML11_RESULT_H