The global value of a variable with buffer-local bindings is also called the default value, because it is the value that is in effect whenever neither the current buffer nor the selected frame has its own binding for the variable.
setq-default access and
change a variable's default value regardless of whether the current
buffer has a buffer-local binding. For example, you could use
setq-default to change the default setting of
paragraph-start for most buffers; and this would work even when
you are in a C or Lisp mode buffer that has a buffer-local value for
The special forms
defconst also set the
default value (if they set the variable at all), rather than any
This function returns symbol's default value. This is the value that is seen in buffers and frames that do not have their own values for this variable. If symbol is not buffer-local, this is equivalent to
symbol-value(see Accessing Variables).
default-boundptells you whether symbol's default value is nonvoid. If
(default-value 'foo)would get an error.
This special form gives each symbol a new default value, which is the result of evaluating the corresponding form. It does not evaluate symbol, but does evaluate form. The value of the
setq-defaultform is the value of the last form.
If a symbol is not buffer-local for the current buffer, and is not marked automatically buffer-local,
setq-defaulthas the same effect as
setq. If symbol is buffer-local for the current buffer, then this changes the value that other buffers will see (as long as they don't have a buffer-local value), but not the value that the current buffer sees.;; In buffer ‘foo’: (make-local-variable 'buffer-local) ⇒ buffer-local (setq buffer-local 'value-in-foo) ⇒ value-in-foo (setq-default buffer-local 'new-default) ⇒ new-default buffer-local ⇒ value-in-foo (default-value 'buffer-local) ⇒ new-default ;; In (the new) buffer ‘bar’: buffer-local ⇒ new-default (default-value 'buffer-local) ⇒ new-default (setq buffer-local 'another-default) ⇒ another-default (default-value 'buffer-local) ⇒ another-default ;; Back in buffer ‘foo’: buffer-local ⇒ value-in-foo (default-value 'buffer-local) ⇒ another-default
This function is like
setq-default, except that symbol is an ordinary evaluated argument.(set-default (car '(a b c)) 23) ⇒ 23 (default-value 'a) ⇒ 23
A variable can be let-bound (see Local Variables) to a value.
This makes its global value shadowed by the binding;
default-value will then return the value from that binding, not
the global value, and
set-default will be prevented from
setting the global value (it will change the let-bound value instead).
The following two functions allow to reference the global value even
if it's shadowed by a let-binding.
This function returns the top-level default value of symbol, which is its value outside of any let-binding.
(defvar variable 'global-value) ⇒ variable (let ((variable 'let-binding)) (default-value 'variable)) ⇒ let-binding (let ((variable 'let-binding)) (default-toplevel-value 'variable)) ⇒ global-value