C++11 initializer list with unique_ptr [duplicate]

Question

Having some issues getting the syntax correct for initializing a vector of unique_ptr.

class Thing {}; class Spider: public Thing {};

Initially tried:

std::vector<std::unique_ptr<Thing>> stuff{std::unique_ptr<Thing>(new Spider)};

But this requires copy constructor (which unique_ptr does not have).

game.cpp:62:46: note: in instantiation of member function 'std::__1::vector<std::__1::unique_ptr<Thing, std::__1::default_delete<Thing> >, std::__1::allocator<std::__1::unique_ptr<Thing, std::__1::default_delete<Thing> > > >::vector' requested here std::vector<std::unique_ptr<Thing>> WestOfStartThings{std::unique_ptr<Thing>(new Spider)}; ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/memory:2510:31: note: copy constructor is implicitly deleted because 'unique_ptr<Thing, std::__1::default_delete<Thing> >' has a user-declared move constructor _LIBCPP_INLINE_VISIBILITY unique_ptr(unique_ptr&& __u) _NOEXCEPT

So I tried to get the move constructor to activate:

std::vector<std::unique_ptr<Thing>> WestOfStartThings{std::move(std::unique_ptr<Thing>(new Spider))};

But still no luck.

game.cpp:62:46: note: in instantiation of member function 'std::__1::vector<std::__1::unique_ptr<Thing, std::__1::default_delete<Thing> >, std::__1::allocator<std::__1::unique_ptr<Thing, std::__1::default_delete<Thing> > > >::vector' requested here std::vector<std::unique_ptr<Thing>> WestOfStartThings{std::move(std::unique_ptr<Thing>(new Spider))}; ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/memory:2510:31: note: copy constructor is implicitly deleted because 'unique_ptr<Thing, std::__1::default_delete<Thing> >' has a user-declared move constructor _LIBCPP_INLINE_VISIBILITY unique_ptr(unique_ptr&& __u) _NOEXCEPT

There's a way to do this but it strikes me as a bit convoluted. — Edward
– Edward, Commented May 13, 2014 at 17:53

Tim Sylvester · Accepted Answer · 2023-04-05 16:26:29Z

Do you care particularly about using initializer lists?

If your goal is just to create the vector above, you can use the following syntax:

std::vector<std::unique_ptr<Thing>> WestOfStartThings; WestOfStartThing.emplace_back(new Spider);

If you do want to use the initializer lists specifically, I believe the syntax is:

std::vector<std::unique_ptr<Thing>> stuff{std::unique_ptr<Thing>{new Spider}};

creating the unique_ptr with an initializer rather than the constructor.

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