与static_assert和boost :: hana相关的Clang编译错误 [英] Clang compile error related to static_assert and boost::hana
问题描述
考虑以下问题,该问题使用 -std = c ++ 14
在Clang 3.8上成功编译。
Consider the following problem which compiles successfully on Clang 3.8 using -std=c++14
.
#include <boost/hana.hpp>
namespace hana = boost::hana;
int main() {
constexpr auto indices = hana::range<unsigned, 0, 3>();
hana::for_each(indices, [&](auto i) {
hana::for_each(indices, [&](auto j) {
constexpr bool test = (i == (j == i ? j : i));
static_assert(test, "error");
});
});
}
测试是完全荒谬的,但这不是重点。现在考虑一个替代版本,其中测试直接放置在 static_assert
中:
The test is quite non-sensical but that is not the point. Consider now an alternative version where the test is directly put inside the static_assert
:
#include <boost/hana.hpp>
namespace hana = boost::hana;
int main() {
constexpr auto indices = hana::range<unsigned, 0, 3>();
hana::for_each(indices, [&](auto i) {
hana::for_each(indices, [&](auto j) {
static_assert((i == (j == i ? j : i)), "error");
});
});
}
现在我遇到一堆编译错误,说
Now I get a bunch of compile errors, saying
错误:引用包含在lambda表达式中的局部变量
i
问题:什么原因导致第二个版本失败?
编辑:这可能是编译器错误吗?我发现,在 static_assert
之前访问 i
时,所有内容都会再次编译:
Could this be a compiler bug? I turns out that when accessing i
before the static_assert
, everything compiles again:
#include <boost/hana.hpp>
namespace hana = boost::hana;
int main() {
constexpr auto indices = hana::range<unsigned, 0, 3>();
hana::for_each(indices, [&](auto i) {
hana::for_each(indices, [&](auto j) {
constexpr auto a = i;
static_assert((i == (j == i ? j : i)), "error");
});
});
}
更新:相同的行为可以在Clang 4.0和当前的开发分支5.0。
更新2:如@LouisDionne所建议,我将其提交为bug: https://bugs.llvm.org/show_bug.cgi?id=33318 。
推荐答案
这是Clang编译器中的错误,因此被确认。这是它的链接: https://bugs.llvm.org/show_bug.cgi ?id = 33318 。
This is a bug in the Clang compiler and was acknowledged as such. Here is the link to it: https://bugs.llvm.org/show_bug.cgi?id=33318.
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