2015-12-25 2:03 GMT+01:00 Eliot Miranda <eliot.miranda@gmail.com>:
Ben,
_,,,^..^,,,_ (phone)
On Dec 4, 2015, at 12:49 AM, Ben Coman <btc@openinworld.com> wrote:
On Fri, Dec 4, 2015 at 4:23 AM, Nicolai Hess <nicolaihess@gmail.com> wrote:
2015-12-03 14:48 GMT+01:00 Ben Coman <btc@openinworld.com>:
On Wed, Dec 2, 2015 at 10:45 PM, Sven Van Caekenberghe <sven@stfx.eu> wrote:
On 02 Dec 2015, at 15:21, Nicolai Hess <nicolaihess@gmail.com>
wrote:
2015-12-02 15:03 GMT+01:00 Ben Coman <btc@openinworld.com>: On Wed, Dec 2, 2015 at 12:38 AM, Tudor Girba <tudor@tudorgirba.com> wrote:
Hi,
On Dec 1, 2015, at 5:13 PM, Max Leske <maxleske@gmail.com> wrote:
@Doru Youâre 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.
I didn't wanted to argue for or against any change. I just wanted to clarify that there are situations in which a generic sum/sum: that throws an error on empty collections and don't assume a null value makes sense.
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.
do that change, I am not against it. Ben just asked for an example and I thought it would be helpful.
It was helpful :) It evolved my thinking. Now thinking further, I wonder how returning 0 will work with applications using units like Aconcagua, and if it would over-complicate things to do something like...
Collection>>sum | sum sample | self isEmpty ifTrue: [ ^ ArithmeticZero ]. sample := self anyOne. sum := self inject: sample into: [ :accum :each | accum + each ]. ^ sum - sample
ArithmeticZero class >> + anObject ^anObject
surely you mean
Collection>>sum ^self inject: ArithmeticZero into: [ :accum :each | accum + each ]
ArithmeticZero class >> + anObject ^anObject
and I'd optimise as Collection>>sum | sum | sum := ArithmeticZero. self do: [ :each | sum := sum + each ]. ^sum
But in with those that want an error and would use either Collection>>sum ^self inject: self anyOne species zero into: [ :accum :each | accum + each ]
or
Collection>>sum | sum | sum := self anyOne species zero. self do: [ :each | sum := sum + each ]. ^sum
Not bad, but the class cannot allways determine the correct zero. For example Matrix is too generic and can't guess about dimensions which are instance specific. So zero should be instance specific. Nicolas