add-functionwhere place function &optional props
This macro is the handy way to add the advice function to the function stored in place (see Generalized Variables).
where determines how function is composed with the existing function, e.g., whether function should be called before, or after the original function. See Advice combinators, for the list of available ways to compose the two functions.
When modifying a variable (whose name will usually end with
you can choose whether function is used globally or only in the current
buffer: if place is just a symbol, then function is added to the
global value of place. Whereas if place is of the form
(local symbol), where symbol is an expression which returns
the variable name, then function will only be added in the
current buffer. Finally, if you want to modify a lexical variable, you will
have to use
Every function added with
add-function can be accompanied by an
association list of properties props. Currently only two of those
properties have a special meaning:
This gives a name to the advice, which
remove-function can use to
identify which function to remove. Typically used when function is an
This specifies how to order the advice, should several pieces of advice be present. By default, the depth is 0. A depth of 100 indicates that this piece of advice should be kept as deep as possible, whereas a depth of -100 indicates that it should stay as the outermost piece. When two pieces of advice specify the same depth, the most recently added one will be outermost.
:before advice, being outermost means that this advice will
be run first, before any other advice, whereas being innermost means
that it will run right before the original function, with no other
advice run between itself and the original function. Similarly, for
:after advice innermost means that it will run right after the
original function, with no other advice run in between, whereas
outermost means that it will be run right at the end after all other
advice. An innermost
:override piece of advice will only
override the original function and other pieces of advice will apply
to it, whereas an outermost
:override piece of advice will
override not only the original function but all other advice applied
to it as well.
If function is not interactive, then the combined function will inherit
the interactive spec, if any, of the original function. Else, the combined
function will be interactive and will use the interactive spec of
function. One exception: if the interactive spec of function
is a function (rather than an expression or a string), then the interactive
spec of the combined function will be a call to that function with as sole
argument the interactive spec of the original function. To interpret the spec
received as argument, use
Note: The interactive spec of function will apply to the combined
function and should hence obey the calling convention of the combined function
rather than that of function. In many cases, it makes no difference
since they are identical, but it does matter for
filter-return, where function.
This macro removes function from the function stored in
place. This only works if function was added to place
function is compared with functions added to place using
equal, to try and make it work also with lambda expressions. It is
additionally compared also with the
name property of the functions added
to place, which can be more reliable than comparing lambda expressions
nil if advice is already in function-def.
remove-function above, instead of advice being the actual
function, it can also be the
name of the piece of advice.
Call the function f for every piece of advice that was added to function-def. f is called with two arguments: the advice function and its properties.
Evaluate the interactive spec just like an interactive call to a function
with such a spec would, and then return the corresponding list of arguments
that was built. E.g.,
(advice-eval-interactive-spec "r\nP") will
return a list of three elements, containing the boundaries of the region and
the current prefix argument.