Dear Julia users,
For my implementation of 2-3 trees (SortOrderDict{K,V}) under development,
it is necessary for the keys to have a total order with the < operator. In
many places in my code, I also want to compare keys using other comparison
operators such as == or <=. It seems that there are three ways to proceed:
(1) The C++ approach: require only that the user of the data structure
provide a '<' operator. All the other comparison operators can be built on
top of '<', with a possible loss of performance. For example, a==b can be
implemented as !(a < b) && !(b < a)
(2) The burden-the-user approach: require the user to provide a complete
set of comparison operators for the key type. This is possibly higher
performance than the C++ approach.
(3) The cool Julia approach: Use code introspection to determine which
operators acting on keys have been provided by the user: only '<', or a
more complete set. On the fly, compile my various routines (insert,
delete, etc) to either use the user-provided complete set, or if not they
are not provided, base everything on the user-provided '<'.
But is the third approach really possible? Can someone show me how to
write a function
function isequal{K}(k1::K, k2::K)
so that if only <(K,K) (but not ==(K,K)) is available, then the function is
compiled as !(k1<k2)&&!(k2<k1), but if ==(K,K) is available, then the
function is compiled as k1==k2 (Note: I don't want this implemented with a
run-time 'if' statement; the loss of performance from 'if' at run-time
would outweigh the benefit.)
Thanks,
Steve Vavasis
P.S. Sorry again for my earlier post in which I complained that
start/done/next was incorrectly designed in Julia; I'll try to keep future
questions more intelligent!
