"SFINAE is Evil"

[Jason House]

I look forward to when you can write more... Are you trying to say SFINAE is needed? I look at the examples and still think probably not. The traits example can be solved cleanly in D, just like enable if. The toughest one is the vector 2 example. I think detection of what is a vector 2 could be done with an interface? The rest of the examples I reaf are SFINAE free.


Bill Baxter Wrote:

> Jason House wrote:
> > I should probably expand this question...
> > 
> > Who uses templates in D? What is the most complex use you've done? Do you ever plan to get more complex? Would SFINAE make your life easier or harder?
> > 
> > I've written templates classes that have one definition, and used static if as needed for specialization. I don't forsee more complex usage and view SFINAE as something that would mask bugs.
> 
> I don't have time to write more right now, but
> Lutz Kettner gives a pretty good examples of using SFINAE here:
> http://www.mpi-inf.mpg.de/~kettner/courses/lib_design_03/notes/meta.html#Constraining
> http://www.mpi-inf.mpg.de/~kettner/courses/lib_design_03/notes/meta.html#Classification
> 
> Certainly the Enable_if template can be replaced by a simple static if.
> Maybe the other one too.
> 
> The main problem I have with templates in D is that traits templates are 
> severely limited by the inability to define specializations for a 
> template in different modules.  Like the IsVector_2 template Lutz talks 
> about.  If all specializations have to be in one file, then the library 
> designer has to know in advance all the types that can ever be used as a 
> Vector2 and clearly that limits the utility of it.
> 
> Maybe this is coming in D2.  I think I did a test recently and it still 
> didn't work.
> 
> 
> 
> --bb