On Wed, Dec 2, 2015 at 10:45 PM, Sven Van Caekenberghe <[email protected]> wrote: > >> On 02 Dec 2015, at 15:21, Nicolai Hess <[email protected]> wrote: >> >> >> >> 2015-12-02 15:03 GMT+01:00 Ben Coman <[email protected]>: >> On Wed, Dec 2, 2015 at 12:38 AM, Tudor Girba <[email protected]> wrote: >> > Hi, >> > >> >> On Dec 1, 2015, at 5:13 PM, Max Leske <[email protected]> wrote: >> >> >> >> @Doru >> >> You’re missing the point: #anyOne *fails* for empty collections. >> > >> > I am not missing the point at all. I am saying that if you want sum: to be >> > generic, it cannot assume a specific Zero object. >> > >> > And sum: should be generic because of its name. >> >> I am missing understanding the other use cases. Can you describe >> further the generic nature of #sum & #sum: ? I would have thought by >> default they only applied to numbers. >> >> sum can be applied to anything that supports #+, not only numbers >> sum: can be applied to any collection with a block that return some object >> that supports #+
To me this is a mis-application of polymorphism, that just because something responds to #+ it should be summable. We have overloaded the semantics of #+ to mean both numeric addition and concatenation/membership, but technically "summation" relates only to numeric addition. https://www.google.com.au/search?q=define+sum&oq=define+sum https://www.google.com.au/search?q=define+concatenate&oq=define+concatenate For example... * KMModifier implements #+ so what is the expected semantic of " { KMModifier shift . KMModifier meta} sum " ? To me this is more of a concatenation/join/union facility rather than numeric addition. (btw, that expression actually fails since KMModifier does not understand minus #- ) . * String implements #+ and " { '1' . '2' } sum " --> '3', so actually its doing numeric addition. However " { 'a' . 'b' } sum " produces an error. So actually there seem some existing problems with summing non-numerics. What examples work? * Trait classes implement both #+ and #- , but the semantic seems more to do with membership than numeric addition. I don't how how to produce an example of using #sum against traits. * Points are summable " { 2@2 . 3@3 } " --> 5@5. But then " 2@2 + 1 " --> 3@3 , so " {} sum " returning 0 would seem to not cause any error in this case. cheers -ben >> >> therefore you can not assume 0 (<- a number) is a proper initial value >> therefore you *need* to work with #anyOne >> and as you can not assume a proper initial value, you can not assume a >> default value for empty collections >> -> it should throw an error. If you (the caller of the function) knows what >> to do with an empty collection you have >> to check, or call inject:into: directly, with a proper initial value. > > I am sorry but I am getting really tired of this, you should read what is > being said. > > I am not suggesting to stop using #anyOne because I like why it is there and > what it can do. > > The change I want is what happens with an empty collection when using the > simplest selector, #sum. > > I do not want to say to some collection of numbers #sumIfEmpty: [0], because > summing numbers starting from zero is the most common case and everybody > expects that, hence the unary selector fits. > > I want the less common cases to use the more complicated API, as in some > collection of colors #sumIfEmpty: [ Color black ] > > In my book that is common sense API design. > > Doing that I do no take anything away, because today you already have to make > sure the collection is not empty. > > The only change would be in the error behaviour. I think that is a reasonable > price to pay. Instead of having #anyOne fail, it will say that #+ cannot add > 0 to some object, and in a comment we can point to the alternative API. > > http://izquotes.com/quote/242740 right ? > >> cheers -ben >> >> > >> >>> On 01 Dec 2015, at 15:31, Esteban A. Maringolo <[email protected]> >> >>> wrote: >> >>> >> >>> I don't want to be heretic (or too orthodox), but why not to delegate >> >>> this behavior to other class (an iterator maybe?). >> >>> >> >>> It's too tempting adding these convenience methods to Collection >> >>> and/or subclasses, but anything that requires an explicit protocol of >> >>> its elements is wrong, IMO. >> >>> >> >>> something like aCollection arithmetic sum: [...] or.... aCollection >> >>> arithmetic avg. >> >> >> >> >> >> Interesting thought! >> > >> > +100 >> > >> > Doru >> > >> >>> >> >>> My two cents for this. >> >>> >> >>> Regards! >> >>> >> >>> >> >>> Esteban A. Maringolo >> >>> >> >> >> >> >> > >> > -- >> > www.tudorgirba.com >> > >> > "Every thing has its own flow." >> > >> > >> > >> > >> > > >
