Annex D (normative) Compatibility features [depr]

D.15 Deprecated shared_­ptr observers [depr.util.smartptr.shared.obs]

The following member is defined in addition to those members specified in [util.smartptr.shared]:
namespace std {
  template<class T> class shared_ptr {
  public:
    bool unique() const noexcept;
  };
}
bool unique() const noexcept;
Returns: use_­count() == 1.