The g:value structure is a variable container that consists of a type identifier and a specific value of that type. The type identifier within a g:value instance determines the type of the associated value. To create an undefined g:value instance, simply create a zero-filled g:value instance. To initialize the g:value instance, use the g:value-init function. A g:value instance cannot be used until it is initialized. These examples demonstrate some of the features.

(defun example-gvalue ()
  ;; Declare two variables of type g:value
  (gobject:with-values (value1 value2)
    ;; Initialization, setting and reading a value of type g:value
    (g:value-set value1 "string" "gchararray")
    (format t "value1 = ~a~%" (g:value-get value1))
    (format t "gtype  = ~a~%" (g:value-type value1))
    (format t "name   = ~a~%~%" (g:value-type-name value1))


    ;; The same for the second value
    (g:value-init value2 "gchararray")
    (setf (g:value-get value2) "a second string")
    (format t "value2 = ~a~%" (g:value-get value2))
    (format t "gtype  = ~a~%" (g:value-type value2))
    (format t "name   = ~a~%~%" (g:value-type-name value2))


    ;; Reuse value1 for an integer
    (g:value-unset value1)
    (g:value-set value1 42 "gint" )
    (format t "value1 = ~a~%" (g:value-get value1))
    (format t "gtype  = ~a~%" (g:value-type value1))
    (format t "name   = ~a~%~%" (g:value-type-name value1))


    ;; Some test functions
    (assert (g:value-holds value1 "gint"))
    (format t "value holds integer is ~a~%" (g:value-holds value1 "gint"))
    (format t "value is integer ~a~%~%" (g:type-is-value "gint"))))