Re: Minimal Distance (Re: Where is Manhattan Dispatch discussion?)
TSa wrote: BTW, what is a flack? See http://en.wikipedia.org/wiki/Flak_%28disambiguation%29 Originally, (FL)ug(a)bwehr (K)anone -- German 88mm anti-aircraft cannon of WWII. Subsequently, any anti-air gun or cannon, particularly when fired at a position rather than aimed at a particular target. Presently: [[ oproer, samenscholing, Tumult, schiamazzo ]] Criticism, ado, alarm, excitement, noise, grief, hullabaloo, angst, wailing and gnashing of teeth, din, clamor, hubbub, rumpus, tumult, uproar, disturbance, objection, consternation, meshugas, narrichkeit, shemozzle, furor. =Austin
Re: Minimal Distance (Re: Where is Manhattan Dispatch discussion?)
On 2008 May 7, at 4:21, TSa wrote: BTW, what is a flack? He's using flak (shrapnel; usual usage catching flak over ...) without understanding it. Coming back to how C++ handles static overloading. How is the sort order of (int *), (int ), (int), (const int *), (const int ), (const int), (int * const) and (const int * const)? I'm too lazy to look up the details, sorry. Been a long time, but I thought C++ compilers threw up their arms in despair if multiple conversion paths of the same length existed (that is, it could use (D)(B)A or (D)(C)A). That said, (int ) and (const int) are identical to (int) for dispatch purposes[*] and (int *) is a completely different type which could only be used if something provided a conversion for it, which would be unusual. [*] The const modifier corresponds to is ro and the is like aliasing a name with :=, in Perl6 terms; neither is actually part of the type. That said, const can be used as a constraint (like a Perl6 subset type; not sure about . But note that C++ has been updated several times since I last looked, and I may well be misremembering even the old standard. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH
Minimal Distance (Re: Where is Manhattan Dispatch discussion?)
Mark A. Biggar mark-at-biggar.org |Perl 6| wrote: To do multi method dispatch, you want to select the method that best matches the parameters in the call. One way to do that is to define a measure for distances between types and they use the method that's at the minimum distance. One simple measure is that a type is distance 0 from itself and distance 1 from it's immediate super-types, distance 2 from the immediate super-types of it's immediate super-types, etc. When dispatching over a single parameter picking the method at the minimum distance is the usual most specific type match. But when you want to do multi-method dispatch, you need some rule to combine the various distances of the individual parameters into a single measure value, then pick the method at the minimum distance by that combined measure. Manhattan Distance or Taxicab Distance is the rule that the combined distance is just the simple unweighted sum of the individual parameter distances. The is named after the fact that a taxi must follow the streets and to go 3 block north and 4 blocks west it must travel 7 blocks not the 5 blocks of the euclidean distance. OK, so basically the fit is the sum of the fits of all the parameters. If form A has a distance of 2 for the first argument and 5 for the second, and form B has a distance of 0 for the first and 10 for the second, form A is better. I heard this term come up the other day with respect to matching value types =and= other attributes such as rw or ref-ness. I thought he meant that these were different directions like streets and avenues, of one parameter. I have problems with a simple sum. The distance is artificially inflated if you make lots of small derivation steps vs one large change. The concept of derivation steps is ill-defined for parameterized types and types that change virtual type names during derivation so there is no subtype relationship. In C++, which must be resolved at compile time, the overloading resolution mechanism demands that =every= parameter be at least as good of a match, and one strictly better match. So the implementation never guesses if worse-left/better-right is a better fit than better-left/worse-right. However, you are assured that everything is brought to your attention at program build time, before run time, so complaining is not as serious as a run-time error where you might prefer DWIM. --John
Re: Minimal Distance (Re: Where is Manhattan Dispatch discussion?)
HaloO, John M. Dlugosz wrote: In C++, which must be resolved at compile time, the overloading resolution mechanism demands that =every= parameter be at least as good of a match, and one strictly better match. So the implementation never guesses if worse-left/better-right is a better fit than better-left/worse-right. However, you are assured that everything is brought to your attention at program build time, before run time, so complaining is not as serious as a run-time error where you might prefer DWIM. Perl 6 is the same, just at runtime with actual types of actual objects. That's it. Regards, TSa. -- The unavoidable price of reliability is simplicity -- C.A.R. Hoare Simplicity does not precede complexity, but follows it. -- A.J. Perlis 1 + 2 + 3 + 4 + ... = -1/12 -- Srinivasa Ramanujan
Re: Minimal Distance (Re: Where is Manhattan Dispatch discussion?)
On Tuesday 06 May 2008 10:38:38 John M. Dlugosz wrote: I have problems with a simple sum. The distance is artificially inflated if you make lots of small derivation steps vs one large change. The concept of derivation steps is ill-defined for parameterized types and types that change virtual type names during derivation so there is no subtype relationship. Those are precisely my objections. I'm not a fan of derivation in general, but I've never understood how changing MMD resolution based on degree of derivation didn't break Liskov. (Damian tried to explain it to me at least once, but he's smarter than I am and I didn't get it.) -- c
Re: Minimal Distance (Re: Where is Manhattan Dispatch discussion?)
On Tue, May 06, 2008 at 08:20:40PM +0200, TSa wrote: HaloO, John M. Dlugosz wrote: In C++, which must be resolved at compile time, the overloading resolution mechanism demands that =every= parameter be at least as good of a match, and one strictly better match. So the implementation never guesses if worse-left/better-right is a better fit than better-left/worse-right. However, you are assured that everything is brought to your attention at program build time, before run time, so complaining is not as serious as a run-time error where you might prefer DWIM. Perl 6 is the same, just at runtime with actual types of actual objects. That's it. Indeed, Perl 6 threw out Manhattan distance a couple years ago. Do we have to spec everything that Perl 6 ever was but isn't now? :) Larry
Re: Minimal Distance (Re: Where is Manhattan Dispatch discussion?)
TSa Thomas.Sandlass-at-barco.com |Perl 6| wrote: HaloO, John M. Dlugosz wrote: In C++, which must be resolved at compile time, the overloading resolution mechanism demands that =every= parameter be at least as good of a match, and one strictly better match. So the implementation never guesses if worse-left/better-right is a better fit than better-left/worse-right. However, you are assured that everything is brought to your attention at program build time, before run time, so complaining is not as serious as a run-time error where you might prefer DWIM. Perl 6 is the same, just at runtime with actual types of actual objects. That's it. Regards, TSa. Then why is everyone against no worse for all parameters, rather than summing?
Re: Minimal Distance (Re: Where is Manhattan Dispatch discussion?)
Larry Wall larry-at-wall.org |Perl 6| wrote: On Tue, May 06, 2008 at 08:20:40PM +0200, TSa wrote: HaloO, John M. Dlugosz wrote: In C++, which must be resolved at compile time, the overloading resolution mechanism demands that =every= parameter be at least as good of a match, and one strictly better match. So the implementation never guesses if worse-left/better-right is a better fit than better-left/worse-right. However, you are assured that everything is brought to your attention at program build time, before run time, so complaining is not as serious as a run-time error where you might prefer DWIM. Perl 6 is the same, just at runtime with actual types of actual objects. That's it. Indeed, Perl 6 threw out Manhattan distance a couple years ago. Do we have to spec everything that Perl 6 ever was but isn't now? :) Larry No, just point me to what it says now. Or the scraps so I can collect them together and say it during my productive period. When I mentioned this before, there was big flack over mentioning the way C++ did it. I think that must have been miscommunicated, since I wasn't even talking about summing all the arguments when he brought up Manhattan dispatch.
