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File 0004-Improve-description-of-cast-macros-for-Ruby.patch of Package swig (Revision 1a6b0c9f16974343b3e16d5c697a7a39)

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From cf53e727267e1f275a413804395092d8172e480a Mon Sep 17 00:00:00 2001
From: Thomas Reitmayr <treitmayr@devbase.at>
Date: Sat, 4 Jan 2020 18:21:10 +0100
Subject: [PATCH 4/4] Improve description of cast macros for Ruby

The macros for casting function pointers are now fully described and also
clarify why the macros act transparently for C even before Ruby 2.7.

In addition, an "if (CPlusPlus)" was removed in the code generator for
global variables in order to keep the distinction between C and C++ in
one place, which is at the definition of said macros.
---
 Lib/ruby/rubyhead.swg   | 32 ++++++++++++++++++++++++--------
 Source/Modules/ruby.cxx | 12 +++++-------
 2 files changed, 29 insertions(+), 15 deletions(-)

diff --git a/Lib/ruby/rubyhead.swg b/Lib/ruby/rubyhead.swg
index 89d6f1466296..bf4e36248ecb 100644
--- a/Lib/ruby/rubyhead.swg
+++ b/Lib/ruby/rubyhead.swg
@@ -98,17 +98,33 @@
 
 
 /*
- * Need to be very careful about how these macros are defined, especially
- * when compiling C++ code or C code with an ANSI C compiler.
+ * The following macros are used for providing the correct type of a
+ * function pointer to the Ruby C API.
+ * Starting with Ruby 2.7 (corresponding to RB_METHOD_DEFINITION_DECL being
+ * defined) these macros act transparently due to Ruby's moving away from
+ * ANYARGS and instead employing strict function signatures.
  *
- * VALUEFUNC(f) is a macro used to typecast a C function that implements
- * a Ruby method so that it can be passed as an argument to API functions
- * like rb_define_method() and rb_define_singleton_method().
+ * Note: In case of C (not C++) the macros are transparent even before
+ * Ruby 2.7 due to the fact that the Ruby C API used function declarators
+ * with empty parentheses, which allows for an unspecified number of
+ * arguments.
  *
- * VOIDFUNC(f) is a macro used to typecast a C function that implements
- * either the "mark" or "free" stuff for a Ruby Data object, so that it
- * can be passed as an argument to API functions like Data_Wrap_Struct()
+ * PROTECTFUNC(f) is used for the function pointer argument of the Ruby
+ * C API function rb_protect().
+ *
+ * VALUEFUNC(f) is used for the function pointer argument(s) of Ruby C API
+ * functions like rb_define_method() and rb_define_singleton_method().
+ *
+ * VOIDFUNC(f) is used to typecast a C function that implements either
+ * the "mark" or "free" stuff for a Ruby Data object, so that it can be
+ * passed as an argument to Ruby C API functions like Data_Wrap_Struct()
  * and Data_Make_Struct().
+ *
+ * SWIG_RUBY_VOID_ANYARGS_FUNC(f) is used for the function pointer
+ * argument(s) of Ruby C API functions like rb_define_virtual_variable().
+ *
+ * SWIG_RUBY_INT_ANYARGS_FUNC(f) is used for the function pointer
+ * argument(s) of Ruby C API functions like st_foreach().
  */
 #if defined(__cplusplus) && !defined(RB_METHOD_DEFINITION_DECL)
 #  define PROTECTFUNC(f) ((VALUE (*)(VALUE)) f)
diff --git a/Source/Modules/ruby.cxx b/Source/Modules/ruby.cxx
index fcbcb7a5c1ba..48b0efab36cd 100644
--- a/Source/Modules/ruby.cxx
+++ b/Source/Modules/ruby.cxx
@@ -2270,13 +2270,11 @@ public:
       Delete(setname);
     }
 
-    /* define accessor method */
-    if (CPlusPlus) {
-      Insert(getfname, 0, "VALUEFUNC(");
-      Append(getfname, ")");
-      Insert(setfname, 0, (use_virtual_var) ? "SWIG_RUBY_VOID_ANYARGS_FUNC(" : "VALUEFUNC(");
-      Append(setfname, ")");
-    }
+    /* define accessor methods */
+    Insert(getfname, 0, "VALUEFUNC(");
+    Append(getfname, ")");
+    Insert(setfname, 0, (use_virtual_var) ? "SWIG_RUBY_VOID_ANYARGS_FUNC(" : "VALUEFUNC(");
+    Append(setfname, ")");
 
     String *s = NewString("");
     switch (current) {
-- 
2.26.0

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