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#ifndef RUBY3_ATTR_NOALIAS_H /*-*-C++-*-vi:se ft=cpp:*/
#define RUBY3_ATTR_NOALIAS_H
/**
* @file
* @author Ruby developers <[email protected]>
* @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 RUBY3_HAS_DECLSPEC_ATTRIBUTE(noalias)
# define RUBY3_ATTR_NOALIAS() __declspec(noalias)
#else
# define RUBY3_ATTR_NOALIAS() /* void */
#endif
#endif /* RUBY3_ATTR_NOALIAS_H */
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