英文:
C2x: what is the rationale for alignas to be a keyword rather than a macro?
问题
1990年，P.J. Plauger写道（已加重标识）：
标准C为您提供了额外的安全级别。这是我所知的其他语言标准中没有的级别。它承诺，如果您避免使用某些名称集，您将不会遇到冲突。因此，标准C使编写高度可移植的应用程序变得更加容易。
在C11中，关键字_Alignas（例如）引入了伴随的宏alignas，定义在<stdalign.h>中。在这里，我们可以看到关键字是_Alignas，而不是alignas（因为在C11之前，alignas未被保留）。因此，不会与可能的用户定义的alignas发生冲突。
然而，在C2x中，alignas是一个关键字，<stdalign.h>不提供任何内容（而C2x对__alignas_is_defined宏没有提及 - 有缺陷吗？）。这意味着在C2x中，任何包含用户定义的alignas的预C2x代码都将导致语义违规，因此会破坏向后兼容性。
问题：
- 这是否意味着自C2x以来，“您将不会遇到冲突”不再成立？
alignas（例如）作为关键字而不是宏的原因是什么？
英文:
In 1990 P.J. Plauger wrote (emphasis added):
> Standard C offers you an additional level of security, however. It is a level
offered in no other language standard that I know. It promises that if you avoid
certain sets of names, you will experience no collisions. Thus, Standard C makes
it that much easier to write highly portable applications.
In C11 keyword _Alignas (for example) was introduced with the accompanying macro alignas defined in <stdalign.h>. Here we see that the keyword is _Alignas, not alignas (since in pre-C11 alignas is not reserved). Hence, there is no collision with possible user-defined alignas.
However, in C2x the alignas is a keyword and <stdalign.h> provides no content (and C2x says nothing about __alignas_is_defined macro -- defect?). It means that in C2x any pre-C2x code containing user-defined alignas will cause semantics violation and, hence, breaks backward compatibility.
Questions:
- Does it mean that since C2x the "you will experience no collisions" does not hold any longer?
- What is the rationale for
alignas(for example) to be a keyword rather than a macro?
答案1
得分: 4
以下是翻译好的部分：
提案中指出，关于新关键字的命名策略已经与之前的标准版本存在不一致之处，有些关键字使用非保留名称（如 const、inline）进行集成，而其他一些则以下划线大写形式集成。对于其中一些关键字，通过一组库头文件来确保使用小写形式。
此外，提案中还提到，为了保持兼容性，将使用与C++相同的关键字命名，因为有些关键字起初源自C++语言，后来才添加到C中。
英文:
The proposal for these change (available at https://open-std.org/JTC1/SC22/WG14/www/docs/n2934.pdf) argues that the naming strategy in regards to new keywords has already been inconsistent with previous standard versions:
> some were integrated using non-reserved names (const, inline) others
were integrated in an underscore-capitalized form. For some of them, the use of the lower-case form then
is ensured via a set of library header files.
Further using the same keyword naming as C++ (for compatibility purposes) is also mentioned in the proposal, since some keywords originated in that language and were later added to C.
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