The following code (reduced for context) is taken from n3092
[expr.prim.lambda], 5.1.2/13, where it states:
"A lambda expression appearing in a default argument shall not implicitly or
explicitly capture and entity."
/cygdrive/d/CPPProjects/nano/gcc_bugs $cat _5_1_2_13.cpp
// file: _5_1_2_13.cpp
void f2() {
int i = 1;
// ...
void g5(int = ([]{ return sizeof i; })());
}
gcc-4.5.0 fails this code with the following error messages.
12:51:47 Paul bibbi...@jijou
/cygdrive/d/CPPProjects/nano/gcc_bugs $i686-pc-cygwin-gcc-4.5.0 -Wall
-save-temps -std=c++0x -c _5_1_2_13.cpp
_5_1_2_13.cpp: In lambda function:
_5_1_2_13.cpp:6:37: error: local variable i may not appear in this context
_5_1_2_13.cpp:6:40: error: return-statement with a value, in function returning
'void'
_5_1_2_13.cpp: In function void f2():
_5_1_2_13.cpp:6:44: error: default argument for int <anonymous> has type
void
_5_1_2_13.cpp:4:8: warning: unused variable i
Appearance of the local variable i in this context is valid on the grounds
that, in the first instance, the operand to sizeof is an unevaluated operand
(as per 5.3.3./1 [expr.sizeof]) and hence (as per 3.2/2 [basic.def.odr]) its
presence here does not constitute a use (which would otherwise require it to be
explicitly or implicitly captured, the latter according to 5.1.2/11). However,
5.1.2/7 should still apply - "The lambda-expression's compound-statement yields
the function body (8.4) of the function call operator, but for the purposes of
name lookup (3.4), [...] the compound-statement is considered in the context of
the lambda-expression."
12:54:21 Paul bibbi...@jijou
/cygdrive/d/CPPProjects/nano/gcc_bugs $i686-pc-cygwin-gcc-4.5.0 -v
Using built-in specs.
COLLECT_GCC=i686-pc-cygwin-gcc-4.5.0
COLLECT_LTO_WRAPPER=/opt/gcc-4.5.0/libexec/gcc/i686-pc-cygwin/4.5.0/lto-wrapper.exe
Target: i686-pc-cygwin
Configured with: ./configure --prefix=/opt/gcc-4.5.0 --enable-bootstrap
--enable-version-specific-runtime-libs --enable-static --enable-shared
--enable-shared-libgcc --disable-__cxa_atexit --with-gnu-ld --with-gnu-as
--with-dwarf2 --disable-sjlj-exceptions --enable-languages=c,c++
--disable-symvers --enable-libgomp --enable-libssp --enable-threads=posix
--with-arch-i686 --with-tune=generic
Thread model: posix
gcc version 4.5.0 (GCC)
--
Summary: [C++0x] name lookup failure on un-used local variable in
lambda compound-statement
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: paul dot bibbings at gmail dot com
GCC host triplet: i686-pc-cygwin
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43886
