lambda - Retaining a pointer by extending the life of capture -


this question has answer here:

is possible extend life of unique_ptr capturing in lambda , extending life of lambda?

i tried out getting syntax errors a=move(a) expression.

#include <cstdio> #include <functional> #include <memory> #include <iostream>  using namespace std;  struct {   a() { cout << "a()" << endl; }  ~a() { cout << "~a()" << endl; } };  int main() {   std::function<void ()> f;   {     std::unique_ptr<a> a(new a());     f = [a=move(a)] () mutable { return; };   }   return 0; }

well problem code std::function. not move friendly needs callable copy constructible/assignable lambda not because of use of move type, unique_ptr in example.

there many examples out there can provide move friendly version of std::function.

i have come here quick, hacky, , error prone "working on machine" version of same:

#include <memory> #include <iostream> #include <type_traits>   struct {   a() { std::cout << "a()" << std::endl; }  ~a() { std::cout << "~a()" << std::endl; } };  template <typename functor> struct holder {     static void call(char* sbo) {         functor* cb = reinterpret_cast<functor*>(sbo);         cb->operator()();     }      static void deleter(char* sbo) {         auto impl = reinterpret_cast<functor*>(sbo);         impl->~functor();     }  };  template <typename sign> struct function;  template <> struct function<void()> {     function() = default;     ~function() {         deleter_(sbo_);     }      template <typename f>     void operator=(f&& f)     {         using c = typename std::decay<f>::type;         new (sbo_) c(std::forward<f>(f));         call_fn_ = holder<c>::call;         deleter_ = holder<c>::deleter;     }      void operator()() {         call_fn_(sbo_);     }      typedef void(*call_ptr_fn)(char*);     call_ptr_fn call_fn_;     call_ptr_fn deleter_;     char sbo_[256] = {0,}; };  int main() {   function<void()> f;   {       std::unique_ptr<a> a(new a());       f = [a=move(a)] () mutable { return; };   }   std::cout << "destructor should not called before this" << std::endl;   return 0; }

to try out yourself: http://coliru.stacked-crooked.com/a/60e1be83753c0f3f


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