Next: Future Local Variables, Previous: Buffer-Local Variables, Up: Variables
Just as variables can have buffer-local bindings, they can also have
frame-local bindings. These bindings belong to one frame, and are in
effect when that frame is selected. Frame-local bindings are actually
frame parameters: you create a frame-local binding in a specific frame
by calling modify-frame-parameters and specifying the variable
name as the parameter name.
To enable frame-local bindings for a certain variable, call the function
make-variable-frame-local.
Enable the use of frame-local bindings for variable. This does not in itself create any frame-local bindings for the variable; however, if some frame already has a value for variable as a frame parameter, that value automatically becomes a frame-local binding.
If variable does not have a default value, then calling this command will give it a default value of
nil. If variable already has a default value, that value remains unchanged.If the variable is terminal-local, this function signals an error, because such variables cannot have frame-local bindings as well. See Multiple Displays. A few variables that are implemented specially in Emacs can be buffer-local, but can never be frame-local.
This command returns variable.
Buffer-local bindings take precedence over frame-local bindings. Thus,
consider a variable foo: if the current buffer has a buffer-local
binding for foo, that binding is active; otherwise, if the
selected frame has a frame-local binding for foo, that binding is
active; otherwise, the default binding of foo is active.
Here is an example. First we prepare a few bindings for foo:
(setq f1 (selected-frame))
(make-variable-frame-local 'foo)
;; Make a buffer-local binding for foo in `b1'.
(set-buffer (get-buffer-create "b1"))
(make-local-variable 'foo)
(setq foo '(b 1))
;; Make a frame-local binding for foo in a new frame.
;; Store that frame in f2.
(setq f2 (make-frame))
(modify-frame-parameters f2 '((foo . (f 2))))
Now we examine foo in various contexts. Whenever the
buffer `b1' is current, its buffer-local binding is in effect,
regardless of the selected frame:
(select-frame f1)
(set-buffer (get-buffer-create "b1"))
foo
⇒ (b 1)
(select-frame f2)
(set-buffer (get-buffer-create "b1"))
foo
⇒ (b 1)
Otherwise, the frame gets a chance to provide the binding; when frame
f2 is selected, its frame-local binding is in effect:
(select-frame f2)
(set-buffer (get-buffer "*scratch*"))
foo
⇒ (f 2)
When neither the current buffer nor the selected frame provides a binding, the default binding is used:
(select-frame f1)
(set-buffer (get-buffer "*scratch*"))
foo
⇒ nil
When the active binding of a variable is a frame-local binding, setting
the variable changes that binding. You can observe the result with
frame-parameters:
(select-frame f2)
(set-buffer (get-buffer "*scratch*"))
(setq foo 'nobody)
(assq 'foo (frame-parameters f2))
⇒ (foo . nobody)