On 2012-02-10 02:47, bearophile wrote:
Some more comments about the conference.
--------------------------
About "Variadic Templates are Funadic" by Andrei Alexandrescu fun talk:
I have had to see it at only 1-1.1X speed, to understand the language.
I can't see the laser spot in the video :-(
Thank you to Walter for designing D varidic templates in a simpler way. C++11
variadic templates look too much complex and over-engineered (example: the
lockstep expansion seems a bit crazy).
Slide 21: I didn't know that default is OK as first switch case too :-)
Even the questions&answers part of this talk was interesting enough.
------------------
About Bjarne Stroustrup and Andrew Sutton "A Concept Design for C++":
Regarding this code in Slide 12:
template<Number Num> Num gsqrt(Num);
gsqrt(2); // fine
gsqrt("Silly!"); // error: char* is not a Number
In D template constraints have two (or more) different usages:
1) To just remove a template from the pool of the usable ones;
2) In other situations only one template is present, and its constraints are a
way to give it some static typing. In this case I'd like better error messages.
Once this patch is applied:
https://github.com/D-Programming-Language/dmd/pull/692
you are able to write something like this, that isn't exceptionally nice
looking, but it's useful (it's going to make Phobos code a bit more hairy, but
the user is going to see some better error messages):
template IsNumberWithError(T, string file, int line) {
enum bool IsNumberWithError = is( ...
static if (!IsNumberWithError)
__ctfeWriteln(file, "(", line, "): '", typeid(T), "' is not a
number.");
}
double gsqrt(T)(T x) if (IsNumberWithError!(T, __FILE__, __LINE__)) { /*...*/ }
Wouldn't this be possible:
template IsNumberWithError(T, string file = __FILE__, int line = __LINE__) {
enum bool IsNumberWithError = is( ...
static if (!IsNumberWithError)
__ctfeWriteln(file, "(", line, "): '", typeid(T), "' is not a
number.");
}
double gsqrt(T)(T x) if (IsNumberWithError!(T)) { /*...*/ }
__FILE__ and __LINE__ would be picked up from the "calling" point and
not the declaration point of IsNumberWithError. We already have this in
some cases.
--
/Jacob Carlborg
