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91 lines
4.1 KiB
C++
91 lines
4.1 KiB
C++
#ifndef RUBY3_ATTR_NOEXCEPT_H /*-*-C++-*-vi:se ft=cpp:*/
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#define RUBY3_ATTR_NOEXCEPT_H
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/**
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* @file
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* @author Ruby developers <ruby-core@ruby-lang.org>
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* @copyright This file is a part of the programming language Ruby.
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* Permission is hereby granted, to either redistribute and/or
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* modify this file, provided that the conditions mentioned in the
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* file COPYING are met. Consult the file for details.
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* @warning Symbols prefixed with either `RUBY3` or `ruby3` are
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* implementation details. Don't take them as canon. They could
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* rapidly appear then vanish. The name (path) of this header file
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* is also an implementation detail. Do not expect it to persist
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* at the place it is now. Developers are free to move it anywhere
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* anytime at will.
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* @note To ruby-core: remember that this header can be possibly
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* recursively included from extension libraries written in C++.
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* Do not expect for instance `__VA_ARGS__` is always available.
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* We assume C99 for ruby itself but we don't assume languages of
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* extension libraries. They could be written in C++98.
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* @brief Defines #RUBY3_ATTR_NOEXCEPT.
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*
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* This isn't actually an attribute in C++ but who cares...
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*
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* Mainly due to aesthetic reasons, this one is rarely used in the project.
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* But can be handy on occasions, especially when a function's noexcept-ness
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* depends on its calling functions.
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*
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* ### Q&A ###
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*
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* - Q: Can a function that raises Ruby exceptions be attributed `noexcept`?
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*
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* - A: Yes. `noexcept` is about C++ exceptions, not Ruby's. They don't
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* interface each other. You can safely attribute a function that raises
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* Ruby exceptions as `noexcept`.
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*
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* - Q: How, then, can I assert that a function I wrote doesn't raise any Ruby
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* exceptions?
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*
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* - A: `__attribute__((__leaf__))` is for that purpose. A function attributed
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* as leaf can still throw C++ exceptions, but not Ruby's. Note however,
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* that it's extremely difficult -- if not impossible -- to assert that a
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* function doesn't raise any Ruby exceptions at all. Use of that
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* attribute is not recommended; mere mortals can't properly use that by
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* hand.
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*
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* - Q: Does it make sense to attribute an inline function `noexcept`?
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*
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* - A: I thought so before. But no, I don't think they are useful any longer.
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*
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* - When an inline function attributed `noexcept` actually doesn't throw
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* any exceptions at all: these days I don't see any difference in
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* generated assembly by adding/removing this attribute. C++ compilers
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* get smarter and smarter. Today they can infer if it actually throws
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* or not without any annotations by humans (correct me if I'm wrong).
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*
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* - When an inline function attributed `noexcepr` actually _does_ throw an
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* exception: they have to call `std::terminate` then (C++ standard
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* mandates so). This means exception handling routines are actually
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* enforced, not omitted. This doesn't impact runtime performance (The
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* Itanium C++ ABI has zero-cost exception handling), but does impact on
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* generated binary size. This is bad.
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*/
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#include "ruby/impl/compiler_since.h"
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#include "ruby/impl/has/feature.h"
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/** Wraps (or simulates) C++11 `noexcept` */
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#if ! defined(__cplusplus)
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# /* Doesn't make sense. */
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# define RUBY3_ATTR_NOEXCEPT(_) /* void */
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#elif RUBY3_HAS_FEATURE(cxx_noexcept)
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# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
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#elif defined(__GXX_EXPERIMENTAL_CXX0X__) && __GXX_EXPERIMENTAL_CXX0X__
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# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
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#elif defined(__INTEL_CXX11_MODE__)
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# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
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#elif RUBY3_COMPILER_SINCE(MSVC, 19, 0, 0)
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# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
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#elif __cplusplus >= 201103L
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# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
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#else
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# define RUBY3_ATTR_NOEXCEPT(_) /* void */
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#endif
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#endif /* RUBY3_ATTR_NOEXCEPT_H */
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