[PATCH] smartset: add a "toset" method

[Jun Wu]

Excerpts from Jun Wu's message of 2017-06-03 13:54:18 -0700:
> Excerpts from Augie Fackler's message of 2017-06-03 16:25:52 -0400:
> > I like where you're headed with this, but I think I'd rather have
> > classes with an efficient way to produce a set implement toset
> > themselves and leave the default implementation as set(self) so we can
> > avoid the spooky action at a distance implied by this hasattr().
> 
> The problem is the lack of ability to customize "set(smartset)" logic in the
> Python language. "set" will always treat "smartset" as an iterable, which
> makes the operation O(N log N) even if we have O(1) fast path.
> 
> Between syntactic simplicity and ability to have fast code path, I want to
> choose the latter.
> 
> For "hasattr", do you mean we might need to do hasattr(x, 'toset')? That
> looks like a sign of poorly designed APIs (sometimes return a smartset,
> sometimes return a set, so you never know what "x" is). It shouldn't happen
> in a clean codebase.

Sorry. I misunderstood the whole paragraph. I'll move "toset" from
"abstractsmartset" to subclasses.

Good advice by the way!