GoingNative 2012 to be livestreamed tomorrow - part 2

[Jacob Carlborg]

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