Move FFI::DataConverter to Ruby

* Include DataConverter in StructByReference in Ruby code to simplify
  ordering.

ext/ffi_c/StructByReference.c

@@ -172,19 +172,13 @@ sbr_from_native(VALUE self, VALUE value, VALUE ctx)
 void
 rbffi_StructByReference_Init(VALUE moduleFFI)
 {
-    /*
-     * Document-class: FFI::StructByReference
-     * This class includes {FFI::DataConverter} module.
-     */
     rbffi_StructByReferenceClass = rb_define_class_under(moduleFFI, "StructByReference", rb_cObject);
     rb_global_variable(&rbffi_StructByReferenceClass);
-    rb_include_module(rbffi_StructByReferenceClass, rb_const_get(moduleFFI, rb_intern("DataConverter")));
-
+
     rb_define_alloc_func(rbffi_StructByReferenceClass, sbr_allocate);
     rb_define_method(rbffi_StructByReferenceClass, "initialize", sbr_initialize, 1);
     rb_define_method(rbffi_StructByReferenceClass, "struct_class", sbr_struct_class, 0);
     rb_define_method(rbffi_StructByReferenceClass, "native_type", sbr_native_type, 0);
     rb_define_method(rbffi_StructByReferenceClass, "to_native", sbr_to_native, 2);
     rb_define_method(rbffi_StructByReferenceClass, "from_native", sbr_from_native, 2);
 }
-

ext/ffi_c/ffi.c

@@ -74,8 +74,6 @@ Init_ffi_c(void)
     /* FFI::Type needs to be initialized before most other classes */
     rbffi_Type_Init(moduleFFI);
 
-    rbffi_DataConverter_Init(moduleFFI);
-
     rbffi_ArrayType_Init(moduleFFI);
     rbffi_LastError_Init(moduleFFI);
     rbffi_Call_Init(moduleFFI);
@@ -95,4 +93,3 @@ Init_ffi_c(void)
     rbffi_Types_Init(moduleFFI);
     rbffi_MappedType_Init(moduleFFI);
 }
-

ext/ffi_c/rbffi.h

@@ -44,7 +44,6 @@ extern void rbffi_Type_Init(VALUE ffiModule);
 extern void rbffi_Buffer_Init(VALUE ffiModule);
 extern void rbffi_Invoker_Init(VALUE ffiModule);
 extern void rbffi_Variadic_Init(VALUE ffiModule);
-extern void rbffi_DataConverter_Init(VALUE ffiModule);
 extern VALUE rbffi_AbstractMemoryClass, rbffi_InvokerClass;
 extern int rbffi_type_size(VALUE type);
 extern void rbffi_Thread_Init(VALUE moduleFFI);
@@ -54,4 +53,3 @@ extern void rbffi_Thread_Init(VALUE moduleFFI);
 #endif
 
 #endif	/* RBFFI_RBFFI_H */
-

lib/ffi/data_converter.rb

@@ -0,0 +1,37 @@
+module FFI
+  # This module is used to extend somes classes and give then a common API.
+  #
+  # Most of methods defined here must be overriden.
+  module DataConverter
+    # Get native type.
+    #
+    # @overload native_type(type)
+    #  @param [String, Symbol, Type] type
+    #  @return [Type]
+    #  Get native type from +type+.
+    #
+    # @overload native_type
+    #  @raise {NotImplementedError} This method must be overriden.
+    def native_type(type = nil)
+      if type
+        @native_type = FFI.find_type(type)
+      else
+        native_type = @native_type
+        unless native_type
+          raise NotImplementedError, 'native_type method not overridden and no native_type set'
+        end
+        native_type
+      end
+    end
+
+    # Convert to a native type.
+    def to_native(value, ctx)
+      value
+    end
+
+    # Convert from a native type.
+    def from_native(value, ctx)
+      value
+    end
+  end
+end

lib/ffi/ffi.rb

@@ -29,6 +29,7 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 require 'ffi/platform'
+require 'ffi/data_converter'
 require 'ffi/types'
 require 'ffi/library'
 require 'ffi/errno'

lib/ffi/struct.rb

@@ -368,4 +368,9 @@ def array_layout(builder, spec)
       end
     end
   end
+
+  # This class includes the {FFI::DataConverter} module.
+  class StructByReference
+    include DataConverter
+  end
 end