on Tue Apr 03 2012, Pyry Jahkola <pyry.jahkola-AT-iki.fi> wrote:
Not to my knowledge (or correct me if it does!). I just acquired this habit from the way the C++11 standard library defined constants like the following in the FDIS:
namespace std { template <class T, T v> struct integral_constant { static constexpr T value = v; typedef T value_type; typedef integral_constant<T,v> type; constexpr operator value_type() { return value; } }; }
Hm. I don't know. I wonder what the purpose of those four characters is?
6) Defining function result and result type at once.
Totally. I have used
// RETURNS() is used to avoid writing boilerplate "->decltype(x) { return x; }" phrases. // // USAGE: auto function(<arguments>) RETURNS(<some-expression>);
I like the trick of requiring a semicolon here.
It makes editors behave, anyway.
Probably it's a good idea to incorporate noexcept: (...)
True. I decided to postpone the use of noexcept until I get other things to work, so I'm still missing all the little tricks there are with noexcept. (Keen to hear about them in May!)
Well, it certainly can't hurt to add the clause when everything's deduced anyway.
It can't be used with recursive definitions like here, though:
// template <typename A, typename B, typename... C> // auto operator()(A const & a, B const & b, C const &... c) const -> // RETURNS(mul_()(a * b, c...))
// --> Error: invalid use of incomplete type mul_
Heh, try (*this) instead of mul_(). That works until you try to incorporate noexcept as suggested above (at least on GCC 4.7).
Yep, same thing on clang: as soon as I enable noexcept in the RETURNS(...) macro, it gives "error: invalid use of 'this' outside of a nonstatic member function".
// ****** workaround ****** static mul_ get() noexcept { return mul_(); }
I'm not sure which one is correct here, GCC or Clang, but but this trick had a similar result: "error: calling 'get' with incomplete return type 'mul_'".
The only alternative way I could fix it was to define a function returning a reference, e.g.:
struct mul_ { // ...
static mul_ const & get() noexcept; };
constexpr mul_ mul = {};
inline mul_ const & mul_::get() noexcept { return mul; }
very annoying.
Indeed.
I think it's a GCC bug: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52869
7) Counted template recursion.
Isn't it a bit slicker to do this by creating an argument pack of integers and expanding that with get<Is>(t)... ?
Oh, sure! I wonder how I missed that. Yes, converting a template argument pack into an equal-length index sequence is very useful.
Don't feel bad; I "missed it" too, until learned about it from someone else ;-) -- Dave Abrahams BoostPro Computing http://www.boostpro.com