[英]Recursion with generic lambda functions in C++14
I came across this question, where the answer describes nice detail about how can the generic lambda functions be used to replace the std::function
technique and how to rewire the stop condition to enable the return type deduction. 我碰到了这个问题, 答案在其中详细描述了如何使用通用Lambda函数代替
std::function
技术以及如何重新连接停止条件以启用返回类型推导。
Based on the above I created the following working example: 基于上述内容,我创建了以下工作示例:
#include <cstdio>
void printSeq(unsigned start) {
auto recursion = [](auto&& self, const char* format, unsigned current) {
printf(format, current);
if(!current)
return static_cast<void>(printf("\n"));
else
self(self, ", %u", current - 1);
};
recursion(recursion, "%u", start);
}
int main() {
return (printSeq(15), 0);
}
My question is that what's the advantage using auto&&
over the auto&
in this case? 我的问题是,在这种情况下,使用
auto&&
相对于auto&
有什么优势? Should I use the std::move
here? 我应该在这里使用
std::move
吗?
auto&
is lvalue only. auto&
仅是左值。
This matters little until you refactor and replace the lvalue recursive object with a temporary proxy memoizer, for example. 直到您重构并用临时代理备注器替换左值递归对象为止,这无关紧要。
auto&&
is harmless, and means "I do not mind if this is a temprary or whatever, just don't make a copy", which expresses meaning well here. auto&&
是无害的,意思是“我不介意这是临时的还是其他东西,只是不要复制”,在这里很好地表达了意思。 auto&
states "No temporaries allowed!" auto&
指出“不允许临时使用!” Sometimes you want to exclude temporaries when making a reference, but it is rare. 有时您在引用时要排除临时对象,但这很少见。
auto const&
, auto
and auto&&
should be your bread and butter. auto const&
, auto
和auto&&
应该是您的面包和黄油。
Only use auto&
if your operation is explicitly about writing and you are ok with excluding proxy references. 仅当您的操作明确涉及编写并且可以排除代理引用时,才使用
auto&
。
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