std.gregorian contribution

[Andrei Alexandrescu]

On 05/17/2010 03:16 PM, Steven Schveighoffer wrote:
> Comparing splitByOneOf(str, "; ")) to splitter(str, set(';', ' ')), I
> see one major difference here -- "; " is a literal, set(';', ' ') is not.
>
> I would expect that 'set' as a generic set type would implement it's
> guts as some sort of tree/hash, which means a lot of overhead for a
> simple argument. With the literal version, the notation is in the
> function, not the type. While it seems rather neat, the overhead should
> be considered.
>
> A compromise:
>
> foreach(x; splitter(str, either("; ")))
>
> Which can be implemented without heap activity.

These are good points. They have gone through my mind as well, but 
lately I've started to take a somewhat more liberal view of containers. 
For example, I'm thinking that Set!T (which would be the type returned 
by set()) could automatically use arrays and linear search for small 
sets. Other special cases come to mind, such as the small array 
optimization. In other words Set!T would not have a guaranteed 
implementation, but instead exploit magnitude to choose among a spectrum 
of implementation alternatives.

Of course using a different name such as either() is even better for the 
implementation because it can make additional implementation dictated by 
the restricted use of either(). For example either() could return a 
FixedSet!T that does not accept adding new members and is optimized 
accordingly.


Andrei