foreign-slot-value object slot-name &key type object-type copy-foreign-object => value
(setf foreign-slot-value) value object slot-name &key type object-type copy-foreign-object => value
Either an instance of or a pointer to an FLI structure.
The name of the slot of object to be accessed.
The type of
object
. Specifying
type
makes accessing the object faster. If the specified type is different to the actual type,
foreign-slot-value
returns the value of the object in the format of
type
where possible.
The FLI structure type that contains slot-name . If this is passed, the compiler might be able to optimize the access to the slot. If this is omitted, the object type is determined dynamically from object .
This option is only important when dealing with slots which are aggregate FLI types, and cannot be returned by value. The recognized values are
t
,
nil
and
:error
:
If
copy-foreign-object
is
t
,
foreign-slot-value
makes a copy of the aggregate slot of the object pointed to by
pointer
and returns the copy.
If
copy-foreign-object
is
nil
,
foreign-slot-value
returns the aggregate slot of the object directly.
If
copy-foreign-object
is
:error
then
foreign-slot-value
signals an error. This is the default value for
copy-foreign-object
.
The function
foreign-slot-value
returns the value of a slot in a specified object. An error is signaled if the slot is an aggregate type and
copy-foreign-object
is not set accordingly. Use foreign-slot-pointer to access such aggregate slots.
The function
(setf foreign-slot-value)
can be used to set the value of a slot in a structure, as shown in the example below.
In the following example a foreign structure is defined, an instance of the structure is made with
my-pos
pointing to the instance, and
foreign-slot-value
is used to set the
y
slot of the object to 10.
(fli:define-c-struct POS
(x :int)
(y :int)
(z :int))
(setq my-pos (fli:allocate-foreign-object :type 'POS))
(setf (fli:foreign-slot-value my-pos 'y) 10)
The next forms both return the value of the
y
slot at
my-pos
, which is 10.
(fli:foreign-slot-value my-pos 'y)
(fli:foreign-slot-value my-pos 'y :object-type 'pos)
See the LispWorks User Guide section "Optimizing your code" for an example showing how to inline foreign slot access.