On 09/17/2010 02:25 AM, Ed Smith-Rowland wrote:
I am slowly working on user defined literals for C++-0x.
Thanks! Please send future patches to gcc-patches and me directly.
Looking over your patch, I see you're doing a significant amount of it
in the parser, which is incorrect; the draft says that a user-defined
literal is a single preprocessing token, so
1.2QQ
(one token) is different from
1.2 QQ
(two tokens).
Anyway, I managed to parse things like
long double
operator"" _foo(long double x) { return 2.0L * x; }
The result is a normal function that I can either call like
operator "" _foo(1.2L);
or just
_foo(1.2L);
You shouldn't be able to call it as just _foo(1.2L); an operator name is
different from a normal function name.
1. A warning or error if a user chooses a suffix that gcc uses. I was
surprised that 'w', 'q', 'i', 'j' and several others were used by gcc for
floats. I won't be the only one.
The standard is clear that implementations get first crack at these but it
shouldn't be a mystery or a surprise when things don't work as expected.
2. Should we at least pedwarn about user not starting a suffix with an underscore? Probably. Non-underscore suffixen are reserved to the implementation
but I think a user should be able to use one if it's not used by gcc
though the user risks non-portability and potential but unlikely future
breakage.
Can you point me to the relevant wording? I'm not finding it.
3. The big one: Getting the integer(long long) and float(long double) suffixes
that are not used by gcc out of the preprocessor. Then we can build the calls.
Yep, I think we want a new CPP token type for user-defined literals that
encapsulates both the raw literal and the suffix.
4. If, for long long and long double the usual signature is not found, first look
for a: _suffix(char*) and failing that: template<char...> _suffix(). So we'll
need to make the lookup of these two signatures more complex.
Right, this will need a new overload resolution function. 2.14.5 tells
you how it works; look at the overload set, see if it contains a
particular signature, and build up a normal call as appropriate.
Jason
