c++ - 关于默认可构造性的差异

Question

Clang 和 GCC 似乎不同意什么使类型默认可构造。 GCC在这里错了吗？标准的正式定义是不是对此没有明确说明？

#include <concepts>

class base {
protected:
    base() = default;
};

struct der : base {
    using base::base;
    der(int) {}
};

der d; // constexpr base::base() is protected within this context
static_assert(std::semiregular<der>); // fails on GCC

Live example

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JHBonarius 和 alagner 提供了所要求的信息，引用了已经很好地涵盖了细节的现有资源。现在，我认为最好将这个问题更多地指向 Clang 的偏离行为。我已经启动了错误报告流程，并将在此处发布任何跟进。

Answer 1

正如我们在评论中讨论的那样，GCC 似乎实现了标准权利(尽管这似乎违反直觉):

C++ 标准，10.3.3.2

Each using-declarator in a using-declaration introduces a set ofdeclarations into the declarative region in which theusing-declaration appears. The set of declarations introduced by theusing-declarator is found by performing qualified name lookup (6.4.3,13.2) for the name in the using-declarator, excluding functions that are hidden as described below. If the using-declarator does not name aconstructor, the unqualified-id is declared in the declarative regionin which the using-declaration appears as a synonym for eachdeclaration introduced by the using-declarator. [ Note: Only thespecified name is so declared; specifying an enumeration name in ausing-declaration does not declare its enumerators in theusing-declaration’s declarative region. — end note ] If theusing-declarator names a constructor, it declares that the classinherits the set of constructor declarations introduced by theusing-declarator from the nominated base class.

请注意 factory method按预期工作。

编辑:它已经被问过并且answered ;)