Comment by eklitzke

The author writes "this might be why there is std::make_shared", but that's not really why it exists. When you create a std::shared_ptr it needs to allocate memory for a control block structure (which tracks the reference count) as well as the memory for the object itself. If you write std::shared_ptr<Foo>(new Foo) this will result in two memory allocations, one for the Foo object and the other for the std::shared_ptr control block. If you write std::make_shared<Foo>() then a single allocation will happen which has enough space for both the control block and the Foo object, and then placement new is used to initialize the memory for both structures. So std::make_shared exists to reduce the number of memory allocations that are being made, not for the reason suggested here.