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To specify which kinds of braces you want auto-newlines put around,
you set the style variable c-hanging-braces-alist
. Its
structure and semantics are described in this section. Details of how
to set it up, and its relationship to CC Mode’s style system are given
in Style Variables.
Say you wanted an auto-newline after (but not before) the following ‘{’:
if (foo < 17) {
First you need to find the syntactic context of the brace—type a RET before the brace to get it on a line of its own28, then type C-c C-s. That will tell you something like:
((substatement-open 1061))
So here you need to put the entry (substatement-open . (after))
into c-hanging-braces-alist
.
If you don’t want any auto-newlines for a particular syntactic symbol,
put this into c-hanging-braces-alist
:
(brace-entry-open)
If some brace syntactic symbol is not in c-hanging-brace-alist
,
its entry is taken by default as (before after)
—insert a
newline both before and after the brace. In place of a
“before/after” list you can specify a function in this alist—this
is useful when the auto newlines depend on the code around the brace.
This variable is an association list which maps syntactic symbols to
lists of places to insert a newline. See Association
Lists in GNU Emacs Lisp Reference Manual. The key of each element is the
syntactic symbol, the associated value is either nil
, a list,
or a function.
The syntactic symbols that are useful as keys in this list are
brace-list-intro
, statement-cont
,
inexpr-class-open
, inexpr-class-close
, and all the
*-open
and *-close
symbols. See Syntactic Symbols,
for a more detailed description of these syntactic symbols, except for
inexpr-class-open
and inexpr-class-close
, which aren’t
actual syntactic symbols. Elements with any other value as a key get
ignored.
The braces of anonymous inner classes in Java are given the special
symbols inexpr-class-open
and inexpr-class-close
, so that
they can be distinguished from the braces of normal classes29.
Note that the aggregate constructs in Pike mode, ‘({’, ‘})’, ‘([’, ‘])’, and ‘(<’, ‘>)’, do not count as brace lists in this regard, even though they do for normal indentation purposes. It’s currently not possible to set automatic newlines on these constructs.
The value associated with each syntactic symbol in this association list is called an action, which can be either a list or a function which returns a list. See Custom Braces, for how to use a function as a brace hanging action.
The list action (or the list returned by action when it’s
a function) contains some combination of the symbols before
and
after
, directing CC Mode where to put newlines in
relationship to the brace being inserted. Thus, if the list contains
only the symbol after
, then the brace hangs on the right side
of the line, as in:
// here, open braces always `hang' void spam( int i ) { if( i == 7 ) { dosomething(i); } }
When the list contains both after
and before
, the braces
will appear on a line by themselves, as shown by the close braces in
the above example. The list can also be empty, in which case newlines
are added neither before nor after the brace.
If a syntactic symbol is missing entirely from
c-hanging-braces-alist
, it’s treated in the same way as an
action with a list containing before
and after
, so
that braces by default end up on their own line.
For example, the default value of c-hanging-braces-alist
is:
((brace-list-open) (brace-entry-open) (statement-cont) (substatement-open after) (block-close . c-snug-do-while) (extern-lang-open after) (namespace-open after) (module-open after) (composition-open after) (inexpr-class-open after) (inexpr-class-close before))
which says that brace-list-open
,
brace-entry-open
and statement-cont
30 braces
should both hang on the right side and allow subsequent text to follow
on the same line as the brace. Also, substatement-open
,
extern-lang-open
, and inexpr-class-open
braces should hang
on the right side, but subsequent text should follow on the next line.
The opposite holds for inexpr-class-close
braces; they won’t
hang, but the following text continues on the same line. Here, in the
block-close
entry, you also see an example of using a function as
an action. In all other cases, braces are put on a line by
themselves.
• Custom Braces |
Also insert a ‘\’ at the end of the previous line if you’re in AWK Mode.
The
braces of anonymous classes produce a combination of
inexpr-class
, and class-open
or class-close
in
normal indentation analysis.
Brace lists
inside statements, such as initializers for static array variables
inside functions in C, are recognized as statement-cont
. All
normal substatement blocks are recognized with other symbols.
Next: Hanging Colons, Previous: Custom Auto-newlines, Up: Custom Auto-newlines [Index]