Bug #16480
closed
Ruby 2.7, C++, and rb_define_method compilation error
Description
I maintain the Rice library which provides constructs for exposing C++ libraries into Ruby. With Ruby 2.7.0 I've got a hard compilation failure that I'm not sure how to fix.[1]
Diving into this, I've found that rb_define_method, when compiled under C++, is now a macro that uses templates to choose the correct overload by the given arity. However, this seems to require a constexpr-compatible use of rb_define_method, making the API unavailable for more dynamic uses[1].
The PR that made these changes is here[3].
I've looked for ways to get around this macro change but have been unable to make anything work. Is there a way I've missed to directly call the underlying C API function or is this now simply not possible with Ruby 2.7.0?
[1] https://github.com/jasonroelofs/rice/issues/119
[2] https://github.com/jasonroelofs/rice/blob/master/rice/detail/method_data.cpp#L78
[3] https://github.com/ruby/ruby/pull/2461
Updated by shyouhei (Shyouhei Urabe) over 4 years ago
- Status changed from Open to Assigned
- Assignee set to nobu (Nobuyoshi Nakada)
It indeed seems to be a bug. For C extensions, that arity argument can be a variable. There is a fallback code. But for C++, there is no way to accept non-constexpr arities. This is a problem.
@nobu (Nobuyoshi Nakada) Can you provide us a workaround? Or revert, because there is no way to support the extension library?
Updated by nobu (Nobuyoshi Nakada) over 4 years ago
Doesn't #undef rb_define_method in that file work?
Updated by jasonroelofs (Jason Roelofs) over 4 years ago
nobu (Nobuyoshi Nakada) wrote:
Doesn't
#undef rb_define_methodin that file work?
Ah yes it looks like it does and thanks for putting together the PR.
Updated by nobu (Nobuyoshi Nakada) over 4 years ago
- Status changed from Assigned to Closed
The arities must be eventually compile-time constants for the nature.
I think this case is quite special, and it is resolved in that project.