在 C++14 中,由于 constexpr
不再是隐式 const
,constexpr
成员函数是否可以修改类的数据成员:
struct myclass
{
int member;
constexpr myclass(int input): member(input) {}
constexpr void f() {member = 42;} // Is it allowed?
};
最佳答案
是的,我相信这个变化是从 proposal N3598: constexpr member functions and implicit const 开始的并最终成为 N3652: Relaxing constraints on constexpr functions 的一部分这改变了部分 7.1.5
段落 3
白名单中函数体中允许的内容:
its function-body shall be = delete, = default, or a compound-statement that contains only
- null statements,
- static_assert-declarations
- typedef declarations and alias-declarations that do not define classes or enumerations,
- using-declarations,
- using-directives,
- and exactly one return statement;
加入黑名单:
its function-body shall be = delete, = default, or a compound-statement that does not contain
- an asm-definition,
- a goto statement,
- a try-block, or
- a definition of a variable of non-literal type or of static or thread storage duration or for which no initialization is performed.
并且还在 C.3.3
部分第 7 条:声明中添加了以下注释:
Change: constexpr non-static member functions are not implicitly const member functions.
Rationale: Necessary to allow constexpr member functions to mutate the object.
Effect on original feature: Valid C++ 2011 code may fail to compile in this International Standard. For example, the following code is valid in C++ 2011 but invalid in this International Standard because it declares the same member function twice with different return types:
struct S { constexpr const int &f(); int &f(); };
关于c++ - 在 C++14 中,constexpr 成员可以更改数据成员吗?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32699007/