[syklemil]

I'm more partial to the first one because it keeps a linear flow downwards, and a uniform structure. The second one kind of drifts off, and reshuffling parts of it is going to be … annoying. IME the dot style lends itself much better to restructuring.

Depending on language you might also have some `.flat_map` option available to drop the `.reduce`.

[itsmeknt]

True! Good point on the restructuring, I haven't thought about it in that way.

I think I like the second approach because the loop behavior seems clearest, which helps me analyze the time complexity or when I want to skim the code quickly.

A syntax like something below would be perfect for me if it existed:

  var favoriteFoodsOfFurryPetsOfFamousAuthorsOfLongChineseBooksAboutHistory = books[i].author.pets[j].favoriteFood.distinct()
    where i = pagecount > 100,
              language == "Chinese",
              subject == "History",
              author.mentions > 10_000
    where j = is_furry == True

[dahauns]

Hm, LINQ query syntax form is kinda going in that direction

  (from book in books
   where book.pagecount > 100 
        && book.language == "Chinese"
        && book.subject == "History"
        && book.author.mentions > 10_000
   from pet in book.author.pets
   where pet.is_furry == true
   select pet.favoriteFood)
  .Distinct()

But it also demonstrates the...erm, chronic "halfassedness" of LINQ's query syntax form with distinct() not available there and having to fall back to method syntax form anyway...

[syklemil]

You would likely approach it in any style with some helper functions once whatever's in the parentheses or ifs starts feeling big. E.g. in the dot style you could

  fn bookFilter(book: Book) -> bool {
   return book.pageCount > 100 and 
     book.language == "Chinese" and 
     book.subject == "History" and
     book.author.mentions > 10_000
  }
  
  var favoriteFoodsOfFurryPetsOfFamousAuthorsOfLongChineseBooksAboutHistory = books
    .filter(bookFilter)
    .flatMap(book => book.author.pets)
    .filter(pet => pet.is_furry)
    .map(pet => pet.favoriteFood)
    .distinct()