C++ 自动推导在 class 构造函数中不起作用

Question

我有两个类:

class string_keys_management {
public:
    string_keys_management(const string_keys_management&) = default;
    string_keys_management(string_keys_management&&) = default;
    string_keys_management& operator=(const string_keys_management&) = default;
    string_keys_management& operator=(string_keys_management&&) = default;
    string_keys_management(const std::initializer_list<std::string>& keys, const std::string &description = "") : keys(keys), description(description) {}
    bool operator==(const std::string &ref) { /*...*/ }
    bool operator!=(const std::string &ref) { /*...*/ }
    bool operator<(const string_keys_management &ref) const { /*...*/ }

private:
    std::vector<std::string> keys;
    std::string description;
};

template <typename V>
class multimap {
public:
    multimap(const std::map<string_keys_management, V> &ref) : values(ref) {}
    multimap& operator=(const std::map<string_keys_management, V> &ref) { values = ref; }
    V& at(const std::string &key) { return values.at(key); }
    void insert(const string_keys_management &keys, V val) { values.insert({keys, val}); }

private:
    std::map<string_keys_management, V> values;
};

当我尝试创建一个 multimap 实例时，当我试图让编译器推导类型时遇到了麻烦：

int main() {
    multimap<std::string> mp = {
            {{{"key1", "key2", "key3"}, "description1"}, "value"},
            {{{"key4", "key5", "key6"}, "description1"}, "value2"}
    };
    return EXIT_SUCCESS;
}

最短的工作方式是：

multimap<std::string> mp = std::map<string_keys_management, std::string>{
        {{{"key1", "key2", "key3"}, "description1"}, "value"},
        {{{"key4", "key5", "key6"}, "description1"}, "value2"}
};

编译器：G++-10.2 C++20.

这是预期的方式，还是编译器问题？
如果它按预期方式运行，哪个规则支持它？

Answer 1

您还缺少一对括号：

multimap<std::string> mp = {{
    { { { "key1", "key2", "key3" }, "description1" }, "value"  },
    { { { "key4", "key5", "key6" }, "description1" }, "value2" }
}};

C++ 自动推导在 class 构造函数中不起作用

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