Comment by wannabe44

IMO it depends on the language… to me, map/collect/etc are useful in languages that have the concept of immutable data, because you can initialize an array with a single call chain, and be sure that nothing after that can modify it.

What I’ve seen in the “for loop” approach that I can’t stand, are things like (pseudo code)

  var a = []
  for x in coll1 {
    a.push(foo(x))
  }

  do_stuff_with(a)

  // … further down the function

  for y in coll2 {
    a.push(bar(y))
  }

  do_other_stuff_with(a)

Reading code like that, is the first call to do_stuff_with(a) a bug, because it’s not fully built from both coll1 and coll2 yet? Or is the second call to do_other_stuff_with(a) a bug because a now contains more stuff than the developer probably thought? Can I safely move both loops next to each other, or does that break something subtle? (In my actual times seeing this, a is really a map of cached key/values or something, and it’s kinda ok that the contents were different, but subtle bugs emerged…)

IMO the sane way to do it is to just not incrementally mutate things like that, and stick with giving things a single place where they’re defined and initialized. Go doesn’t really help you here because there’s no such thing as immutable data. So just adding Map/collect or whatever doesn’t really buy you much.

map functions are very useful for iterating over collections. Most functions iterating over collections are useful, because a lot of the data you're commonly dealing with is collections. And most collections are generic.

> Function literals are verbose and inlining is far less agressive.

> Even python shuns map and filter in favor of comprehensions.

That's the problem of the language design. And Python isn't the best language to turn to for language design

> A for loop is more readable than the lambda soup.

A for loop shoving modified items into a temp variable with append() that is then returned is less readable than a map function transforming data. Too bad Go decided to turn lambdas into unreadable soup.