NAME

       TOID_DECLARE(),    TOID_DECLARE_ROOT(),   TOID(),   TOID_TYPE_NUM(),   TOID_TYPE_NUM_OF(),
       TOID_VALID(),    OID_INSTANCEOF(),    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 confusing and error-prone.  To facilitate type safety, libpmemobj(7) defines a set
       of macros that provide static 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 variable 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_LAYOUT_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 persistent 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>