使用lambda的dectltype作为模板参数

Question

我试图使用lambda的decltype作为模板参数。

auto compare = [](int a, int b){return a < b;};
std::priority_queue<int, std::vector<int>, decltype(compare)> my_queue;

cppreference.com说我可以做到这一点：

// From the cpprefernce.com
auto cmp = [](int left, int right) { return (left ^ 1) < (right ^ 1);};
std::priority_queue<int, std::vector<int>, decltype(cmp)> q3(cmp);

但是当我尝试编译时，我得到了

src/main.cpp:22:64: error: use of deleted function ‘main()::<lambda(int, int)>::<lambda>()’
std::priority_queue<int, std::vector<int>, decltype(compare)> my_queue;
                                                            ^
src/main.cpp:21:18: note: a lambda closure type has a deleted default constructor
auto compare = [](int a, int b){return a < b;};
              ^
src/main.cpp:22:64: note:   when instantiating default argument for call to std::priority_queue<_Tp, _Sequence, _Compare>::priority_queue(const _Compare&, _Sequence&&) [with _Tp = int; _Sequence = std::vector<int>; _Compare = main()::<lambda(int, int)>]
std::priority_queue<int, std::vector<int>, decltype(compare)> my_queue;
                                                            ^

我不明白为什么我不能这样做。我甚至都没有尝试使用lambda的构造函数吗？

Answer 1

我明白了。您必须使用lambda构造priority_queue。

std::priority_queue<int, std::vector<int>, decltype(compare)> my_queue(compare);