template<class T>
struct SingletonPtr< T >

Utility class for creating and using a singleton.

Note

Synchronization level: Thread safe

: This class is lazily initialized on first use. This class has a constexpr default constructor so if it is not used as a non-local variable it will be garbage collected.

: This class would normally be used in a static standalone context. It does not call the destructor of the wrapped object when it is destroyed, effectively ensuring linker exclusion of the destructor for static objects. If used in another context, such as a member of a normal class wanting "initialize on first-use" semantics on a member, care should be taken to call the destroy method manually if necessary.

: If used as a sub-object of a class, that class's own constructor must be constexpr to achieve its exclusion by the linker when unused. That will require explicit initialization of its other members.

: More detail on initialization: Formerly, SingletonPtr had no constructor, so was "zero-initialized" when non-local. So if enclosed in another class with no constructor, the whole thing would be zero-initialized, and linker-excludable. Having no constructor meant SingletonPtr was not constexpr, which limited applicability in other contexts. With its new constexpr constructor, it is now "constant-initialized" when non-local. This achieves the same effect as a standalone non-local object, but as a sub-object linker exclusion is now only achieved if the outer object is itself using a constexpr constructor to get constant-initialization. Otherwise, the outer object will be neither zero-initialized nor constant-initialized, so will be "dynamic-initialized", and likely to be left in by the linker.

Definition at line 112 of file SingletonPtr.h.