Method create

tests/test_smart_ptr.cpp:255–255

    SftVirtBase() = default;
    virtual ~SftVirtBase() = default;
    static std::shared_ptr<SftVirtBase> create() { return std::make_shared<SftVirtBase>(); }
    virtual std::string name() { return "SftVirtBase"; }
};
struct SftVirtDerived : SftVirtBase {