Piotr Rak ha scritto:
>
> I have made hackish implementation of this, which includes
> Alberto Ganesh Barbati extension to proposal, for gcc compiler.
> It still needs some `love'. Maybe soon i will find real time to work
> on that.
That is great! It's really a good thing what you've done.
> It seems that my orginal proposal is slightly harder to implement (in
> gcc), one would have to check just if there is parameter pack in
> template parameter list too.
That's what I was afraid about, when I wrote about "advantages and
disadvantages" in my previous post.
>
> Following example shows status of this patch (and it Works For Me TM):
>
> #include <iostream>
>
> template <char... Chars_>
> struct Foo {
> static const char chars[sizeof...(Chars_)+1];
> };
>
> template <char...Chars_>
> const char
> Foo<Chars_...>::chars[sizeof...(Chars_)+1] = {Chars_...};
>
> template <char B_, char A_, char R_, char Term_>
> struct Bar
> {
> static const char chars[4];
> };
>
> template <char B_, char A_, char R_, char Term_>
> const char
> Bar<B_, A_, R_, Term_>::chars[4] = {B_, A_, R_, Term_};
> int main()
> {
> std::cout << Foo<"foo", '\0'>::chars << std::endl;
> std::cout << Bar<"bar", '\0'>::chars << std::endl;
> }
>
> Compile with -std=c++0x -fstring-template-arguments
Very nice! Very. I like the idea of being able to concatenate string and
character literals in a template argument list.
>
> The know deficiencies are:
> - doesn't handle wide literals (should be easy),
> and unicode literals (not in gcc yet)
I guess the simplest thing is to replace the literal with a sequence of
char, char16_t, char32_t or wchar_t according to the string literal and
let the usual promotion and conversion machinery to happen. Were you
think of something different?
> - I should re****t error in case of "" or L""
Do we need to diagnose an error in this situation? Would expanding to an
empty sequence be impossible or unreasonable?
> - definitly needs testing (DejaGNU here I come!)
If you need help, please contact me privately.
> - and documentation...
If you need help, please contact me privately.
> But overall, it should be enough to see how it feels.
>
> I am not sure if default template arguments should be sup****ted ie:
>
> template <char... Chars_ = "Oink!">
> struct Foo;
>
> Comments welcome :)
Ah! Good point. Currently default template-arguments cannot be specified
for parameter packs. Although the feature is very appealing, I would
leave it at that. Unless we make that a very special case, we would
actually be forced to provide a meaning for the "equivalent" syntax:
template <char... Chars_ = 'O','i','n','k','!'>
struct Foo;
and this would open a Pandora's box, IMHO.
So I guess we should provide wording to disallow literals in default
template-arguments, where replacement doesn't make sense.
>
> Note that, this was first time i've seen gcc sources...
That means gcc sources are very well written or that you are very
skilled or both ;)
> For brave people, patch against gcc trunk, revision 134411
> http://doppler.no-ip.org/~prak/fstring-template-arguments.patch
Thanks! Now it's time to prepare a formal proposal. Let me help you with
that.
Ganesh
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