https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95346
Bug ID: 95346 Summary: [coroutines] coroutine return-type should be initialised with rvalue if different from get_return_object() return-type Product: gcc Version: 10.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: lewissbaker.opensource at gmail dot com Target Milestone: --- If I have the following code: ---------- #include <coroutine> struct task { struct promise_type { task get_return_object(); void return_void(); void unhandled_exception(); std::suspend_always initial_suspend() noexcept; std::suspend_always final_suspend() noexcept; }; }; struct wrapper { using promise_type = task::promise_type; wrapper(task&&); }; wrapper f() { co_return; } ---------- Then building with GCC 10.0 and GCC trunk with -std=c++20 -fcoroutines fails with the following compile-error: x86-64 gcc (trunk) -O3 -std=c++2a -Wall -fcoroutines 1 <Compilation failed> x86-64 gcc (trunk) - 368ms <source>: In function 'wrapper f()': error: cannot bind rvalue reference of type 'task&&' to lvalue of type 'task' 30 | } | ^ note: initializing argument 1 of 'wrapper::wrapper(task&&)' 25 | wrapper(task&&); I think the return-value of a coroutine should be initialised with an rvalue-reference to the object returned from get_return_object() if the two objects have different types. GCC seems to be trying to initialise the return-value using an lvalue-reference to the object returned from get_return_object(). Both Clang and MSVC accept this code, while GCC does not. See https://godbolt.org/z/4RRtaL