以临时方式调用时以产生编译器错误的方式重载方法 [英] Overload a method in a way that generates a compiler error when called with a temporary

问题描述

也许这段代码可以最好地说明我的意图：

Perhaps this piece of code will illustrate my intent best:

#include <array>

template <size_t N>
void f(std::array<char, N> arr)
{
}

template <size_t N>
void f(std::array<char, N>&& arr)
{
    static_assert(false, "This function may not be called with a temporary.");
}

f（）应该为左值而不是右值编译。这段代码适用于MSVC，但是即使从未调用此重载，GCC也会在 static_assert 上跳闸。

f() should compile for lvalues but not for rvalues. This code works with MSVC, but GCC trips on the static_assert even though this overload is never called.

问题有两个：如何用现代C ++正确表达我的意图，为什么编译器会在从未实例化的死模板重载中评估 static_assert ？

So my question is two-fold: how to express my intent properly with modern C++, and why does the compiler evaluate static_assert in a "dead" template overload that's never instantiated?

在线试用： https://godbolt.org/z/ yJJn7_

推荐答案

一种选择是删除 static_assert 而是将该功能标记为已删除。然后，如果您使用右值调用它，则会收到一条错误消息，提示您正在尝试使用已删除的函数

One option is to remove the static_assert and instead mark the function as deleted. Then if you call it with an rvalue you will get an error saying you are trying to use a deleted function

template <size_t N>
void f(const std::array<char, N>& arr)
{

}

template <size_t N>
void f(const std::array<char, N>&& arr) = delete; // used const here just in case we get a const prvalue

int main()
{
    std::array<char, 3> foo{};
    f(foo);
    //f(std::array<char, 3>{}); // error
    return 0;
}

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