mirror of
https://github.com/ruby/ruby.git
synced 2022-11-09 12:17:21 -05:00
58 lines
3 KiB
C++
58 lines
3 KiB
C++
/** \noop-*-C++-*-vi:ft=cpp
|
|
* @file
|
|
* @author Ruby developers <ruby-core@ruby-lang.org>
|
|
* @copyright This file is a part of the programming language Ruby.
|
|
* Permission is hereby granted, to either redistribute and/or
|
|
* modify this file, provided that the conditions mentioned in the
|
|
* file COPYING are met. Consult the file for details.
|
|
* @warning Symbols prefixed with either `RUBY3` or `ruby3` are
|
|
* implementation details. Don't take them as canon. They could
|
|
* rapidly appear then vanish. The name (path) of this header file
|
|
* is also an implementation detail. Do not expect it to persist
|
|
* at the place it is now. Developers are free to move it anywhere
|
|
* anytime at will.
|
|
* @note To ruby-core: remember that this header can be possibly
|
|
* recursively included from extension libraries written in C++.
|
|
* Do not expect for instance `__VA_ARGS__` is always available.
|
|
* We assume C99 for ruby itself but we don't assume languages of
|
|
* extension libraries. They could be written in C++98.
|
|
* @brief Defines #RUBY3_ATTR_NOALIAS.
|
|
*
|
|
* ### Q&A ###
|
|
*
|
|
* - Q: There are seemingly similar attributes named #RUBY3_ATTR_CONST,
|
|
* #RUBY3_ATTR_PURE, and #RUBY3_ATTR_NOALIAS. What are the difference?
|
|
*
|
|
* - A: Allowed operations are different.
|
|
*
|
|
* - #RUBY3_ATTR_CONST ... Functions attributed by this are not allowed to
|
|
* read/write _any_ pointers at all (there are exceptional situations
|
|
* when reading a pointer is possible but forget that; they are too
|
|
* exceptional to be useful). Just remember that everything pointer-
|
|
* related are NG.
|
|
*
|
|
* - #RUBY3_ATTR_PURE ... Functions attributed by this can read any
|
|
* nonvolatile pointers, but no writes are allowed at all. The ability
|
|
* to read _any_ nonvolatile pointers makes it possible to mark ::VALUE-
|
|
* taking functions as being pure, as long as they are read-only.
|
|
*
|
|
* - #RUBY3_ATTR_NOALIAS ... Can both read/write, but only through pointers
|
|
* passed to the function as parameters. This is a typical situation
|
|
* when you create a C++ non-static member function which only concerns
|
|
* `this`. No global variables are allowed to read/write. So this is
|
|
* not a super-set of being pure. If you want to read something, that
|
|
* has to be passed to the function as a pointer. ::VALUE -taking
|
|
* functions thus cannot be attributed as such.
|
|
*/
|
|
#include "ruby/3/has/declspec_attribute.h"
|
|
|
|
/** Wraps (or simulates) `__declspec((noalias))` */
|
|
#if defined(RUBY3_ATTR_NOALIAS)
|
|
# /* Take that. */
|
|
|
|
#elif RUBY3_HAS_DECLSPEC_ATTRIBUTE(noalias)
|
|
# define RUBY3_ATTR_NOALIAS() __declspec(noalias)
|
|
|
|
#else
|
|
# define RUBY3_ATTR_NOALIAS() /* void */
|
|
#endif
|