Issue #11962 has been updated by Kenta Murata.


Can I fix it by the following change?

~~~diff
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 7aabf5b..72523c6 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -874,7 +874,7 @@ struct RBasic {
 VALUE rb_obj_hide(VALUE obj);
 VALUE rb_obj_reveal(VALUE obj, VALUE klass); /* do not use this API to change klass information */

-#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P)
+#if defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P) && !defined(__cplusplus)
 # define RB_OBJ_WB_UNPROTECT_FOR(type, obj) \
     __extension__( \
        __builtin_choose_expr( \
~~~

----------------------------------------
Bug #11962: Ruby 2.3.0 causing compile failure on extensions using a C++ compiler
https://bugs.ruby-lang.org/issues/11962#change-55999

* Author: Sameer Deshmukh
* Status: Open
* Priority: Normal
* Assignee: Nobuyoshi Nakada
* ruby -v: 2.3.0
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
Hello,

I'm a contributor with the SciRuby foundation, and we have a gem called [nmatrix](https://github.com/SciRuby/nmatrix), which is a ruby gem for linear algebra processing in Ruby.

For representing different types of data, nmatrix makes heavy use of C++ templates, which requires compilation with g++. Currently we wrap the code that defines ruby functions at C level in an `extern "C" {}` block in a .cpp file and use g++ to compile the file as a whole.

Upgrading to ruby 2.3.0 has caused a problem because of [this change implemented in the internals of the ruby C API](https://github.com/ruby/ruby/commit/334710c155ad19cfd947ce6bcd7127b97cbe37da#diff-3b256c5581538dcd834697c766a2b1aaR879).

As specified in the GCC docs (https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html) the function "__builtin_choose_expr" (that has been introduced in the latest Ruby C API) is available only for C. Thus the change is rendering our C++ extensions useless.

You can see the compile error being caused in nmatrix here: https://github.com/SciRuby/nmatrix/issues/429

I have come up with [a temporary fix for this](https://github.com/SciRuby/nmatrix/pull/432/files#diff-cc867f54069967617c44c1ca31a5969aR37), but its only patch work and will need to be done by every single extension employing a C++ compiler.

Looking forward to a positive response from you.



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