[phobos] Simplify iota for floating-point types?

[David Simcha]

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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