Dear Julia users,
As I have mentioned in earlier posts, I am working on a 2-3 tree
implementation of a sort-order dict, that is, a dict in which the (key,
value) pairs can be retrieved in the sort-order of the keys. According to
section 2.1.7 of the manual, "for i = I; <body> ; end" translates to:
state = start(I)
while !done(I, state)
(i,state) = next(I,state)
<body>
end
The more obvious way to implement the loop would be to put the body BEFORE
the 'next' statement, and at first I thought that maybe the manual has a
typo. But then I checked the file dict.jl, and I found indeed the code:
done(t::ObjectIdDict, i) = is(next(t,i),())
So this means that every loop iteration over an ObjectIdDict requires two
calls to 'next', one as part of the call to 'done', and a second one to
actually advance the loop.
I also looked at the code for 'done' for Dict in dict.jl, and it appears to
be buggy(??). It does not check whether everything after the current i is
deleted(??)
For a 2-3 tree, the 'next' operation is logarithmic time, so requiring it
twice per loop iteration is undesirable.
Can anyone shed light on why the Julia loop construction is implemented
this way, so that two separate calls to 'next' are necessary? I suppose
that it is possible with additional code complexity to cache the result of
the first call to 'next' inside the state, but what exactly is the
rationale for the current design?
Thanks,
Steve Vavasis
