memory_view.c: Rename private to private_data for C++ (#4812)

* memory_view.c: Rename private to private_data for C++

* doc/memory_view.md: Update document

* Fix doc/memory_view.md

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

doc/memory_view.md

@@ -89,7 +89,7 @@ The MemoryView structure consists of the following members.
     A `ndim` size array consisting of the offsets in each dimension when the MemoryView exposes a nested array.
     This can be `NULL` when the MemoryView exposes a flat array.
 
-- `void *const private`
+- `void *private_data`
 
     The private data that MemoryView provider uses internally.
     This can be `NULL` when any private data is unnecessary.

include/ruby/memory_view.h

@@ -100,7 +100,7 @@ typedef struct {
     const ssize_t *sub_offsets;
 
     /* the private data for managing this exported memory */
-    void *const private;
+    void *private_data;
 } rb_memory_view_t;
 
 typedef bool (* rb_memory_view_get_func_t)(VALUE obj, rb_memory_view_t *view, int flags);

memory_view.c

@@ -210,7 +210,7 @@ rb_memory_view_init_as_byte_array(rb_memory_view_t *view, VALUE obj, void *data,
     view->shape = NULL;
     view->strides = NULL;
     view->sub_offsets = NULL;
-    *((void **)&view->private) = NULL;
+    view->private_data = NULL;
 
     return true;
 }