Re: Recent changes in Range#step behavior

On Mar 26, 2008, at 12:31 PM, Yukihiro Matsumoto wrote:
> OK, makes sense.  Do you mean member? (and its alias include?) should
> always use discrete comparison?

My understanding is that in the general case a range is defined by two  
objects of compatible classes. The objects should define succ() and <=  
or <. The members in the range are derived by applying succ() to the  
first object, and then to the object returned by succ(), etc, until  
the result is no longer <= or < the end of the range.

So, in the general case, all ranges are discrete.

The anomaly is ranges of floats, which you aren't allowed to iterate  
anyway. In that case, member? becomes a comparison that the argument  
is between the limit, because conceptually the range (1.0..2.0)  
contains the infinite number of real values between 1 and 2.

So, yes, I think that all range membership tests should be discrete,  
with float being the special case that you fake it out because  
iterating over the infinite number of values would take too long :)


Dave