Can I avoid copying during the intialization of a std::initializer_list without using raw pointers?

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Category:Languages

Let's say I have several objects declared locally that I want to iterate over using range-based for syntax. This seems to work well, however, it appears that to put the local objects into the initializer_list, a copy is performed. This is bad news for objects like std::shared_ptr for which (as I understand) incrementing the reference count is an atomic operation. The only way I think this can be avoided is by using raw pointers.

#include <iostream> #include <memory>  int main() {     std::shared_ptr<int> ptrInt1 = std::make_shared<int>(1);     std::shared_ptr<int> ptrInt2 = std::make_shared<int>(2);     /* in this loop, ptrInt1 and ptrInt2 are copied before they are binded        to ptrInt, this is ugly since the reference counter needs to temporarily        increased */     for(const std::shared_ptr<int>& ptrInt : {ptrInt1, ptrInt2}) {         std::cerr << *ptrInt << std::endl;     }     /* this solution works, but it feels somewhat ugly having to convert my smart        pointers to raw pointers to avoid the copying, perhaps there is a better        solution ?? */     for(const int* rawPtrInt : {ptrInt1.get(), ptrInt2.get()}) {         std::cerr << *rawPtrInt << std::endl;     }     return 0; } 

Is there a way to iterate over a group of locally declared objects without copying them or resorting to using raw pointers?

 


You can use std::ref to build a list of std::reference_wrappers. This hides the pointer and lets you write the list like

for(const std::shared_ptr<int>& ptrInt : {std::ref(ptrInt1), std::ref(ptrInt2)}) {     std::cerr << *ptrInt << std::endl; } 

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