std.partition is fucked

[Andrei Alexandrescu]

Sean Kelly wrote:
> == Quote from Andrei Alexandrescu (SeeWebsiteForEmail at erdani.org)'s article
>> Sean Kelly wrote:
>>> Andrei Alexandrescu wrote:
>>>> Note how the left edge of result follows the left edge of r, but the
>>>> right edge stays put because partition() returns the right-hand-side
>>>> range. r shrinks from both ends to exhaustion.
>>> So all the elements that satisfy the predicate end up at the end of the
>>> original range instead of the beginning?  Was that an arbitrary choice,
>>> or is there a reason for it?
>> The elements satisfying the predicate are at the beginning, see e.g. the
>> unittests. The range returned is (as always) the right-hand side, i.e.
>> the range containing the elements that don't satisfy the predicate.
> 
> Weird.  I'd always thought that the standard behavior was the opposite.
> That way partition could be passed a lessThan predicate and be used
> for sorting.  Though I guess you can just use a greaterThan predicate
> instead.

Nono, lessThan is a binary predicate whereas partition takes a unary 
predicate. The spec of partition is very simple: do whatever the hell it 
takes to put elements e that satisfy pred(e) before elements that don't.

If you follow the way std.sort uses partition, you'll see that it passes 
a unary predicate that compares for less than against the chosen pivot.


Andrei