workaround for C++ 98 const union problem.

Not the case of recent compilers, but compilers before C++11
rejected ruby.h, like https://ci.appveyor.com/project/ruby/ruby/builds/27225706/job/qjca7dpe204dytbd

This is supposedly because a struct with a member qualified with
a const effectively deletes its default copy constructor, which
is considered as being user-defined somehow.  Not sure where
exactly is the phrase in the C++98 standard who allows such C /
C++ incompatibility though.

1 files changed, 6 insertions, 1 deletions

diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 445b2cd4d3..0bede6ffdd 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -1054,7 +1054,12 @@ struct RArray {
 	    long len;
 	    union {
 		long capa;
-                const VALUE shared_root;
+#if defined(__clang__)      /* <- clang++ is sane */ || \
+    !defined(__cplusplus)   /* <- C99 is sane */     || \
+    (__cplusplus > 199711L) /* <- C++11 is sane */
+                const
+#endif
+                VALUE shared_root;
 	    } aux;
 	    const VALUE *ptr;
 	} heap;