[phobos] Simplify iota for floating-point types?

[Andrei Alexandrescu]

These are reasonable arguments, and I'd agree a lot more if I didn't 
also believe that bidirectional and random access of iota ranges is 
extremely rare. So it looks like we're hurting the common case for the 
sake of a potential but obscure and rarely realized generality.

Andrei

On 12/23/10 12:49 PM, David Simcha wrote:
> I vote for leaving iota as is. Reasoning:
>
> 1. In general, premature micro-optimization is a Bad Thing. A standard
> library should aim to be correct, general and reasonably efficient and
> handle the 95% of cases well. If you need micro-optimization or are
> otherwise in that hardest 5%, you have the core language in which to
> roll your own widget.
>
> 2. In the case of quick and dirty code, the user probably won't care
> much about the speed advantage of using a forward range, and may do
> something silly like eagerly evaluate using array() if he/she needs a
> bidirectional/random access range, thus worsening the performance
> problem instead of solving it.
>
> 3. In the case of higher quality code, iota as it currently stands is
> only a problem in performance critical code that doesn't need anything
> beyond forward access. If someone really needs the speed, it's trivial
> to roll one's own iota equivalent that offers only forward access, or
> even manually inline and hand optimize it for possibly even more speed.
> If the forward range version of iota were the default and someone needed
> the bidirectional/random version, it would be less trivial to roll one's
> own, as the user might miss the subtle details that make Phobos's
> current implementation correct.
>
> On 12/23/2010 1:20 PM, Andrei Alexandrescu wrote:
>> Per the recent discussion comparing D with Lua, tests suggest that
>> iota for double is too slow. This is a necessity if iota is a
>> bidirectional or random-access range. If we allow it to be a forward
>> range, then performance would be significantly increased.
>>
>> Do you agree with making iota for floating-point types a forward range?
>>
>>
>> Andrei
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>
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