为什么要调用dtor（使用匿名/ lambda函数）
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我试图模仿一种最终的效果。所以我认为我应该进行快速的肮脏测试。
这个想法是使用“最重要的” const来停止破坏，并将“ finally”块放入lambda中。但是显然我做错了什么，它在MyFinally（）的末尾被调用。我该如何解决这个问题？
#include <cassert>
template<typename T>
class D{
T fn;
public:
D(T v):fn(v){}
~D(){fn();}
};
template<typename T>
const D<T>& MyFinally(T t) { return D<T>(t); }
int d;
class A{
int a;
public:
void start(){
int a=1;
auto v = MyFinally([&]{a=2;});
try{
assert(a==1);
//do stuff
}
catch(int){
//do stuff
}
}
};
int main() {
A a;
a.start();
}
#include <cassert>
template<typename T>
class D{
T fn; bool exec;
public:
D(T v):fn(v),exec(true){}
//D(D const&)=delete //VS doesnt support this yet and i didnt feel like writing virtual=0
D(D &&d):fn(move(d.fn)), exec(d.exec) {
d.exec = false;
}
~D(){if(exec) fn();}
};
template<typename T>
D<T> MyFinally(T t) { return D<T>(t); }
#define FINALLY(v) auto OnlyOneFinallyPlz = MyFinally(v)
int d;
class A{
public:
int a;
void start(){
a=1;
//auto v = MyFinally([&]{a=2;});
FINALLY([&]{a=2;});
try{
assert(a==1);
//do stuff
}
catch(int){
FINALLY([&]{a=3;}); //ok, inside another scope
try{
assert(a==1);
//do other stuff
}
catch(int){
//do other stuff
}
}
}
};
void main() {
A a;
a.start();
assert(a.a==2);
}
没有找到相关结果
已邀请:
5 个回复
琶竞捆栓
// WRONG! returning a reference to a temporary that will be // destroyed at the end of the function! template<typename T> const D<T>& MyFinally(T t) { return D<T>(t); }template<typename T> class D{ T fn; bool exec; public: D(T v):fn(move(v)),exec(true){} D(D &&d):fn(move(d.fn)), exec(d.exec) { d.exec = false; } ~D(){if(exec) fn();} };template<typename T> D<T> MyFinally(T t) { return D<T>(move(t)); }时，不需要\“ const reference \\”技巧。请参阅此处，了解如何在C ++ 03中使用const引用进行操作。缉康怪
结乳
。class Defer { public: typedef std::function<void()> Executor; Defer(): _executor(DoNothing) {} Defer(Executor e): _executor(e) {} ~Defer() { _executor(); } Defer(Defer&& rhs): _executor(rhs._executor) { rhs._executor = DoNothing; } Defer& operator=(Defer rhs) { std::swap(_executor, rhs._executor); return *this; } Defer(Defer const&) = delete; private: static void DoNothing() {} Executor _executor; };void A::start() { a = 1; Defer const defer([&]() { a = 2; }); try { assert(a == 1); /**/ } catch(...) { /**/ } }夏瓤跋棘
template<typename T> D<T> MyFinally(T t) { D<T> local(t); //create a local variable return local; }const auto & v = MyFinally([&]{a=2;}); //store by const reference函数之前被调用。 另一种不再使用auto关键字的实现：struct base { virtual ~base(){} }; template<typename TLambda> struct exec : base { TLambda lambda; exec(TLambda l) : lambda(l){} ~exec() { lambda(); } }; class lambda{ base *pbase; public: template<typename TLambda> lambda(TLambda l): pbase(new exec<TLambda>(l)){} ~lambda() { delete pbase; } };lambda finally = [&]{a=2; std::cout << \"finally executed\" << std::endl; };你换
template<typename T> std::shared_ptr<D<T>> MyFinally(T t) { return std::shared_ptr<D<T>>(new D<T>(t)); }