TOID_DECLARE(3)

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>