https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95910
--- Comment #2 from Rene Rahn <rene.r...@fu-berlin.de> --- Ok, thanks for the explanation. I do understand the issue now and why it causes the hard error and not an substitution failure. But honestly, given that it works for container because they are wrapped in a ref_view with pointer semantics, makes this very hard to understand. And basically, if you transform something that calls somewhere in the stack a function with auto return type you might not be able to even do `decltype(expression)` to get the return type deduced any more, because the compiler has to instantiate the expression. That makes generic code with auto return types kind of difficult to use, does it? I mean, especially as a library writer I must make sure that the client can use my methods/types in these contexts. And it feels plausible that types are constrained to be mutable somewhere in this context. Is there a general trick to avoid this, except guaranteeing to know the return type before the expression is evaluated? Many thanks for your help!
