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-rw-r--r--include/ruby/impl/attr/pure.h43
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diff --git a/include/ruby/impl/attr/pure.h b/include/ruby/impl/attr/pure.h
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+#ifndef RUBY3_ATTR_PURE_H /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY3_ATTR_PURE_H
+/**
+ * @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_PURE.
+ */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/attribute.h"
+#include "ruby/assert.h"
+
+/** Wraps (or simulates) `__attribute__((pure))` */
+#if RUBY3_HAS_ATTRIBUTE(pure)
+# define RUBY3_ATTR_PURE() __attribute__((__pure__))
+#elif RUBY3_COMPILER_SINCE(SunPro, 5, 10, 0)
+# define RUBY3_ATTR_PURE() _Pragma("does_not_write_global_data")
+#else
+# define RUBY3_ATTR_PURE() /* void */
+#endif
+
+/** Enables #RUBY3_ATTR_PURE iff. #RUBY_NDEBUG. */
+#if RUBY_NDEBUG
+# define RUBY3_ATTR_PURE_ON_NDEBUG() RUBY3_ATTR_PURE()
+#else
+# define RUBY3_ATTR_PURE_ON_NDEBUG() /* void */
+#endif
+
+#endif /* RUBY3_ATTR_PURE_H */