使用lambda的dectltype作爲模板參數

Question

我試圖使用lambda的decltype作爲模板參數。

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

的cppreference.com說，我可以做到這一點：

// 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，當我嘗試編譯，我得到

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; 
                  ^

我不明白爲什麼我不能做這個。我甚至沒有嘗試使用lambda的構造函數嗎？

Answer 1

我想通了。你必須用lambda構造priority_queue。

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