Enable implicit construction for aggregates using {{ ... }}

test/result_error_construct2.cpp

@@ -0,0 +1,57 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <string>
+
+using namespace boost::system;
+
+struct X
+{
+    int a, b;
+};
+
+result<X> fx1()
+{
+    return {{ EINVAL, generic_category() }};
+}
+
+struct Y
+{
+    std::string v;
+};
+
+struct E
+{
+    int v;
+};
+
+result<Y, E> fy1()
+{
+    return {{ 42 }};
+}
+
+int main()
+{
+    {
+        result<X> r = fx1();
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), std::error_code( EINVAL, generic_category() ) );
+    }
+
+    {
+        result<Y, E> r = fy1();
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v, 42 );
+    }
+
+    return boost::report_errors();
+}