NAME

       TOID_DECLARE(),  TOID_DECLARE_ROOT(),  TOID(), TOID_TYPE_NUM(), TOID_TYPE_NUM_OF(), TOID_VALID(), OID_IN‐
       STANCEOF(), TOID_ASSIGN(), TOID_IS_NULL(), TOID_EQUALS(),  TOID_TYPEOF(),  TOID_OFFSETOF(),  DIRECT_RW(),
       D_RW(), DIRECT_RO(), D_RO() - libpmemobj type safety mechanism

SYNOPSIS

              #include <libpmemobj.h>

              TOID_DECLARE(TYPE, uint64_t type_num)
              TOID_DECLARE_ROOT(ROOT_TYPE)
              TOID(TYPE)
              TOID_TYPE_NUM(TYPE)
              TOID_TYPE_NUM_OF(TOID oid)
              TOID_VALID(TOID oid)
              OID_INSTANCEOF(PMEMoid oid, TYPE)
              TOID_ASSIGN(TOID o, VALUE)
              TOID_IS_NULL(TOID o)
              TOID_EQUALS(TOID lhs, TOID rhs)
              TOID_TYPEOF(TOID o)
              TOID_OFFSETOF(TOID o, FILED)
              DIRECT_RW(TOID oid)
              D_RW(TOID oid)
              DIRECT_RO(TOID oid)
              D_RO(TOID oid)

DESCRIPTION

       Operating on untyped object handles, as well as on direct untyped object pointers (void*), may be confus‐
       ing and error-prone.  To facilitate type safety, libpmemobj(7) defines a set of macros that provide stat‐
       ic  type  enforcement,  catching  potential errors at compile time.  For example, a compile-time error is
       generated when an attempt is made to assign a handle to an object of one type to the object handle  vari‐
       able of another type of object.

       The TOID_DECLARE() macro declares a typed OID of user-defined type TYPE and type number type_num.

       The  TOID_DECLARE_ROOT()  macro  declares a typed OID of user-defined type ROOT_TYPE and root object type
       number POBJ_ROOT_TYPE_NUM.

       The TOID() macro declares a handle to an object of type TYPE, where TYPE is the name  of  a  user-defined
       structure.  The typed OID must be declared first using the TOID_DECLARE(), TOID_DECLARE_ROOT(), POBJ_LAY‐
       OUT_TOID(3) or POBJ_LAYOUT_ROOT(3) macros.

       The TOID_TYPE_NUM() macro returns the type number of the type specified by TYPE.

       The  TOID_TYPE_NUM_OF() macro returns the type number of the object specified by oid.  The type number is
       read from the typed OID.

       The TOID_VALID() macro validates whether the type number stored in the object’s metadata is equal to  the
       type number read from the typed OID.

       The OID_INSTANCEOF() macro checks whether the oid is of type TYPE.

       The TOID_ASSIGN() macro assigns the object handle VALUE to typed OID o.

       The TOID_IS_NULL() macro evaluates to true if the object handle represented by o is OID_NULL.

       The  TOID_EQUALS() macro evaluates to true if both the lhs and rhs object handles reference the same per‐
       sistent object.

       The TOID_TYPEOF() macro returns the type of the object handle represented by typed OID o.

       The TOID_OFFSETOF() macro returns the offset of the FIELD member from the start of the object represented
       by o.

       The DIRECT_RW() macro and its shortened form D_RW() return a typed write pointer  (TYPE*)  to  an  object
       represented by oid.  If oid is OID_NULL, the macro evaluates to NULL.

       The  DIRECT_RO()  macro and its shortened form D_RO() return a typed read-only (const) pointer (TYPE*) to
       an object represented by oid.  If oid is OID_NULL, the macro evaluates to NULL.

SEE ALSO

       OID_IS_NULL(3), POBJ_LAYOUT_ROOT(3), POBJ_LAYOUT_TOID(3), libpmemobj(7) and <https://pmem.io>