Name
alx-0003r3 - Add directives #def and #enddef
Category
New directives.
Author
Alejandro Colomar <alx@kernel.org>
Cc: Martin Uecker <uecker@tugraz.at>
Cc: Joseph Myers <josmyers@redhat.com>
Cc: Javier Múgica <javier@aerotri.es>
Cc: Ori Bernstein <ori@eigenstate.org>
Cc: Christopher Bazley <chris.bazley.wg14@gmail.com>
History
<https://www.alejandro-colomar.es/src/alx/alx/wg14/alx-0003.git/>
r0 (2025-03-10):
- Pick stuff from n1410.
r1 (2025-03-11):
- Fix typos.
- Only allow conditional (and null) preprocessing directives
within a replacement body.
- Update wording regarding nesting with if sections.
- Update wording that refers to replacement lists.
Thanks to Joseph for the feedback that led to r1.
r2 (2025-03-14):
- Disallow all preprocessing directives within a replacement
group. Make it equivalent to #define except for not needing
the escape characters to use multiple source lines. This is
the minimal feature, which makes sure we don't add an
underdeveloped feature, but rather a scoped one.
r3 (2025-03-19):
- Define replacement-group directly in terms of pp-tokens, not
in terms of replacement-list.
Description
One thing that gets in the way when writing and sharing macros
is writing (and updating) the trailing \ at the end of each
line. Multi-line macros could be defined with an end delimiter
instead. That would also make syntax highlighting nicer.
Here's the proposed syntax:
#def foo(x)
do {
bar(x);
baz(x);
while (0)
#enddef
Proposed wording
Based on N3467.
6.10.1 Preprocessing directives :: General
@@ Syntax, p1
group-part:
if-section
+ def-section
control-line
text-line
# non-directive
@@ p1, after endif-line
+def-section:
+ def-line replacement-group(opt) enddef-line
+
+def-line:
+ # def identifier new-line
+ # def identifier lparen identifier-list(opt) ) new-line
+ # def identifier lparen ... ) new-line
+ # def identifier lparen identifier-list , ... ) new-line
+
+replacement-group:
+ pp-tokens(opt) new-line
+ replacement-group pp-tokens(opt) new-line
+
+enddef-line:
+ # enddef new-line
6.10.2 Conditional inclusion
@@ Constraints, p4
(that is,
if it is predefined
or if it has been the subject of
-a #define
+a #define or #def
preprocessing directive
without an intervening #undef directive
with the same subject identifier),
6.10.3 Source file inclusion
s/replacement list/& or group/g
6.10.4 Binary resource inclusion
s/replacement list/& or group/g
6.10.5.1 Macro replacement :: General
@@ Constraints, p1
-Two replacement lists
+Two replacement lists or groups
are identical
@@ p2
shall not be redefined
-by another #define preprocessing directive
+by another #define or #def preprocessing directive
unless the second definition is
an object-like macro definition
-and the two replacement lists
+and the two replacement lists or groups
are identical.
...
shall not be redefined
-by another #define preprocessing directive
+by another #define or #def preprocessing directive
unless the second definition is
a function-like macro definition
that has the same number and spelling of parameters,
-and the two replacement lists
+and the two replacement lists or groups
are identical.
@@ p5
The identifiers __VA_ARGS__ and __VA_OPT__
shall occur only in
-the replacement-list
+the replacement list or group
of a function-like macro
@@ Semantics, p7
The identifier immediately following the
-define
+define or def
is called the macro name.
...
Any white-space characters preceding or following
-the replacement list
+the replacement list or group
of preprocessing tokens
are not considered part of the replacement list or group
for either form of macro.
@@ p9
A preprocessing directive of the form
# define identifier replacement-list new-line
+ # def identifier new-line
...
to be replaced by
-the replacement list
+the replacement list or group
of preprocessing tokens
that constitute the remainder of the directive.
-The replacement list
+The replacement list or group
is then rescanned for more macro names
as specified later in this subclause.
@@ p10
A preprocessing directive of the form
# define identifier lparen identifier-list(opt) ) replacement-list new-line
# define identifier lparen ... ) replacement-list new-line
# define identifier lparen identifier-list , ... ) replacement-list new-line
+ # def identifier lparen identifier-list(opt) ) new-line
+ # def identifier lparen ... ) new-line
+ # def identifier lparen identifier-list , ... ) new-line
...
until the new-line character
-that terminates the #define preprocessing directive.
+that terminates the #define preprocessing directive,
+or until the enddef line
+that terminates the #def preprocessing directive.
Each subsequent instance of the function-like macro name
followed by a ( as the next preprocessing token
introduces the sequence of preprocessing tokens
that is replaced by
-the replacement list
+the replacement list or group
in the definition
(an invocation of the macro).
6.10.5.2 Macro replacement :: Argument substitution
s/replacement list/& or group/g
6.10.5.3 Macro replacement :: The # operator
@@ Constraints, p1
Each # preprocessing token
-in the replacement list
+in the replacement list or group
for a function-like macro
shall be followed by a parameter
as the next preprocessing token in the replacement list.
@@ Semantics, p2
If,
-in the replacement list,
+in the replacement list or group,
a parameter is immediately preceded
by a # preprocessing token,
6.10.5.4 Macro replacement :: The ## operator
s/replacement list/& or group/g
6.10.5.5 Macro replacement :: Rescanning and further replacement
s/replacement list/& or group/g
6.10.6 Line control
s/replacement list/& or group/g
6.10.10.1 Predefined macro names :: General
@@ p2
shall be the subject of
-a #define or a #undef
+a #define, #def, or #undef
preprocessing directive.
7.28 Type-generic math <tgmath.h>
@@ p14 (NOTE)
- #define cbrt(X) \
- _Generic((X), \
- long double: _Roundwise_cbrtl, \
- default: _Roundwise_cbrt, \
- float: _Roundwise_cbrtf \
- )(X)
+ #def cbrt(X)
+ _Generic((X),
+ long double: _Roundwise_cbrtl,
+ default: _Roundwise_cbrt,
+ float: _Roundwise_cbrtf
+ )(X)
+ #enddef
J.1 Unspecified behavior
s/replacement list/& or group/g