From 8a8af2a40e87434a49de12a6773de7dc5a4b15e7 Mon Sep 17 00:00:00 2001 From: Eli Zaretskii Date: Tue, 3 Apr 2007 09:50:08 +0000 Subject: [PATCH] (Inline Functions): Describe more disadvantages of defsubst, and make advice against it stronger. --- lispref/functions.texi | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/lispref/functions.texi b/lispref/functions.texi index 045aa454c9c..eedfa8c124f 100644 --- a/lispref/functions.texi +++ b/lispref/functions.texi @@ -1193,17 +1193,22 @@ function except for one thing: when you compile a call to the function, the function's definition is open-coded into the caller. Making a function inline makes explicit calls run faster. But it also -has disadvantages. For one thing, it reduces flexibility; if you change -the definition of the function, calls already inlined still use the old -definition until you recompile them. Since the flexibility of -redefining functions is an important feature of Emacs, you should not -make a function inline unless its speed is really crucial. +has disadvantages. For one thing, it reduces flexibility; if you +change the definition of the function, calls already inlined still use +the old definition until you recompile them. Another disadvantage is that making a large function inline can increase the size of compiled code both in files and in memory. Since the speed advantage of inline functions is greatest for small functions, you generally should not make large functions inline. +Also, inline functions do not behave well with respect to debugging, +tracing, and advising (@pxref{Advising Functions}). Since ease of +debugging and the flexibility of redefining functions are important +features of Emacs, you should not make a function inline, even if it's +small, unless its speed is really crucial, and you've timed the code +to verify that using @code{defun} actually has performance problems. + It's possible to define a macro to expand into the same code that an inline function would execute. (@xref{Macros}.) But the macro would be limited to direct use in expressions---a macro cannot be called with -- 2.39.5