Objects

Most values you have seen so far have been primitive values such as numbers, text, or null.

Objects are different: they can have their own vars and procs attached to them.

In DM, most user-defined objects ultimately descend from /datum, and more specific kinds of objects are described with type paths.

Type Paths

Type paths are how DM names object types.

/obj
/obj/weapon
/obj/weapon/sword

Each extra step in the path makes the type more specific. A /obj/weapon/sword is a kind of /obj/weapon, which is itself a kind of /obj. Just like a file system.

Creating Objects

Use new to create an object.

var/obj/weapon/W = new /obj/weapon

If the variable already has a type, DM can infer the type for new:

var/obj/weapon/W = new

Typed Variables

Typing an object variable is important because it tells the compiler what vars and procs you expect that object to have.

/obj/weapon
  var/title = "Weapon"
  var/damage = 0

/proc/main()
  var/obj/weapon/W = new
  W.title = "Sword"
  W.damage = 15
  world.log << "[W.title] deals [W.damage] damage."

If W were not typed as obj/weapon, the compiler would not know whether title and damage were valid to access.

Checking Types

Sometimes you are given a more general object and need to see whether it is really the kind you want.

For that, use istype():

/obj/weapon
  var/damage = 10

/proc/show_damage(obj/thing)
  if (istype(thing, /obj/weapon))
    var/obj/weapon/W = thing
    world.log << W.damage

Casting

If you want to convert a general object reference into a more specific typed one, astype() can help:

/proc/show_damage(obj/thing)
  var/obj/weapon/W = astype(thing, /obj/weapon)
  world.log << W?.damage

If thing is not actually a /obj/weapon, then W becomes null.

Putting It Together

/obj/weapon
  var/title = "Weapon"
  var/damage = 0

  proc/describe()
    return "[title] deals [damage] damage."

/obj/weapon/sword
  title = "Longsword"
  damage = 15

/proc/print_weapon(obj/thing)
  var/obj/weapon/W = astype(thing, /obj/weapon)
  world.log << W?.describe()

/proc/main()
  var/obj/weapon/sword/my_sword = new
  print_weapon(my_sword)

Objects become much more powerful once you start inheriting from existing types and overriding their behaviour, which is what the next few pages cover.

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