2017-11-07 14:20 GMT+01:00 Denis Kudriashov <dionisiydk@gmail.com>:

I have new question. Why we really need threeWayCompareTo:?

DefaultSortFunction can implement it using standard comparison methods.

But what would the DefaultSortFunction use?

2 among the 3 selectors < = > ?

It's just that we might scan String twice when <=> would do it once, but apart that is OK

2017-11-05 0:37 GMT+01:00 Nicolas Cellier <nicolas.cellier.aka.nice@gmail.com>:

Hi all,

I started a discussion with Denis in a pull request

https://github.com/pharo-project/pharo/pull/430

But since it's going beyond simple code review, it probably has a better place here.

First, I want to say thanks for enriching this original work of Travis Griggs.
http://objology.blogspot.fr/2010/11/tag-sortfunctions-redux.html

http://objology.blogspot.fr/2010/11/tag-sortfunctions.html

Of course, I'm never satisfied.

So I don't really appreciate the rewrite of space ship operator <=> into a more heavy threeWayCompareTo:

In my eyes, it's so obvious that <=> means < or = or > in the context of SortFunction
And also that the order matches the signs

< = >

-1 0 1

IOW result will be -1 if receiver is <, 0 if equal, +1 if superior

#threeWayCompareTo: does not tell as well.

But maybe It's a question of taste and I don't have the same eyes as Pharo people?

To me it's also a question of respect to the original author, don't change a good selector for the sake of changing.

Apart this detail, I wanted to speak about SortByPropertyFunction.
SortByProperty is super usefull for composing / chaining like this:

�� �� population sortBy: #name ascending , #age descending.

But currently, SortByPropertyFunction is allways using the default hardcoded collation <=> ... He he, it's also notice it's shorter to write ;)

Imagine that my properties are neither String nor Magnitude, or they are, but I want a different collation policy, because in French $�� must not be sorted too far from $e.

It could be written quite simply with:

�� ��c sortBy: #name collatedInFrench ascending , #age descending

With current implementation, collatedInFrench would have to use a block (thru a CollatorBlockFunction which is a proxy to the block in a SortFunction disguise):

������ Symbol>>collatedInFrench

�������������� "interpret self as a property"

�������������� ^[:a :b | FrenchCollator collate: (self value: a) with: (self value: b)]

But IMO SortByPropertyFunction should better feed a reified CollatorFunction, or said differently a SortFunction, as Denis said.

������ Symbol>>collatedInFrench

�������������� ^FrenchCollator new onProperty: self

������ SortFunction>>onProperty: aValuable

�������������� ^SortByPropertyFunction sortProperty: aValuable with: self

What do you think?

Nicolas