scala: Ordering.by vs Ordering.on

Question

What is the difference between Ordering.by() and Ordering.on() in Scala?

(Well, one is defined in the trait and the other in the companion object, and the implementation code is also different, but there must be a reason why the language needs both.)

Well, as you said, because one is in the object thus is a factory, and the other in the trait, thus being a combinator. They are both there to help you create newer Ordering instances out of existing ones. — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Oct 12, 2022 at 19:48

Gaël J · Accepted Answer · 2022-10-12 19:51:27Z

3

From the documentation of Ordering.by:

This function is an analogue to Ordering.on where the Ordering[S] parameter is passed implicitly.

Basically the two are the same, it's just a matter of convenience depending of what is your context and what you're working with.

answered Oct 12, 2022 at 19:51

Gaël J

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2 Comments

18446744073709551615 Over a year ago

Can you please provide examples? In what case what is more convenient?

Luis Miguel Mejía Suárez Over a year ago

@18446744073709551615 if you want to create a new ordering out of nowhere, then something like Ordering.by((foo: Foo) => ...) is very convenient, more than doping Ordering[Bar].on(foo => ...) - However, in some other contexts it may be more convenient to call on on an existing instance.

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