Advanced Loops

Basic while and numeric for loops cover a lot of ground, but DM also has some very useful loop forms for working with lists and other collections.

Looping Over Lists

If you already have a list, you can loop over its contents directly:

/proc/main()
  var/list/items = list("crowbar", "wrench", "cable")

  for (var/item in items)
    world.log << item

This is usually cleaner than manually working with indexes.

NOTE: When you loop through a list, DM loops over a copy of that list. If the original list changes during the loop, the current loop will not suddenly start using the new contents.

Typed Loop Variables

Loop variables can have types too.

That means DM will filter out values that do not match the type you asked for:

/datum/coin

/proc/main()
  var/list/mixed = list(
    new /datum/coin,
    "hello",
    5,
    new /datum/coin
  )

  for (var/datum/coin/coin in mixed)
    world.log << "Ooh! A coin!"

Even though mixed contains text and a number, only the /datum/coin values are handled inside the loop.

Looping Over Contents

You can also loop over objects exist in the world and contain things:

for (var/obj/O in turf.contents)
  world << "There's a [O] here."

This is a common ways to find mobs, objs, turfs, and other map objects.

Key/Value Loops

Associative lists can be looped through as key/value pairs:

/proc/main()
  var/list/prices = list(
    "apple" = 2,
    "banana" = 3,
    "pear" = 5
  )

  for (var/name, price in prices)
    world.log << "[name] costs [price]"

This is nicer than writing prices[name] each time when you need both the key and the value.

Labeled `break` and `continue`

When loops get nested, sometimes you want to break out of an outer loop rather than just the innermost one.

DM supports labels for that:

finding_key:
  for (var/mob/M in world)
    for (var/obj/O in M.contents)
      if (O.name == "gold key")
        world << "Found the key on [M]."
        break finding_key

Likewise, continue can jump to the next iteration of a labeled loop:

finding_enemies:
  for (var/mob/M in world)
    for (var/mob/G in world)
      if (M in G.friends)
        continue finding_enemies

    world.log << "[M] has no enemies"

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