https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99273
Bug ID: 99273 Summary: List initialization prefers initializer_list a little too strongly Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: rs2740 at gmail dot com Target Milestone: --- This is basically bug 64665 but closed back in 2015 - I think incorrectly. Reduced test case: #include <initializer_list> struct S { S(int); }; void f(std::initializer_list<S>); int f(int); using T = decltype(f({1})); using T = int; GCC rejects (picking the initializer_list<S> overload); Clang accepts. {1} to initializer_list<S> is a user-defined conversion (https://eel.is/c++draft/over.ics.list#5); {1} to int is a standard conversion - in particular, the identity conversion (https://eel.is/c++draft/over.ics.list#10.1). Since the conversion sequences are not of the same basic form, https://eel.is/c++draft/over.ics.rank#2 controls and says that the latter is better. DR 1467 modified what is now https://eel.is/c++draft/over.ics.rank#3.1 to say that a list initialization sequence that converts to initializer_list is better than any other list-initialization sequence "even if one of the other rules in this paragraph would otherwise apply", but paragraph 3 only applies when the two conversion sequences have the same basic form. In the above example, they don't.