Datums, lists, typepaths, static appearances, and some other objects are represented in Luau as userdata. Certain operations can be performed on these types of objects.

Common metamethods

The following metamethods are defined for all objects.

__tostring(): string

Returns the string representation of the object. This uses BYOND's internal string conversion function.

__eq(other: any): boolean

Compare the equality of two objects. While passing the same object into luau twice will return two references to the same userdata, some DM projects may override the equality operator using an __operator== proc definition.

Datum-like Objects

Datum-like objects include datums themselves, clients (if they have not been redefined to be children of /datum), static appearances, and the world.

__index(index: string): any

Access the member specified by index.

If index is a valid var for the object, the index operation will return that var's value. If the var getting wrapper proc is set, the operation will instead call that proc with the arguments (object, index).

For objects other than static appearances, if index is a valid proc for the object, the operation will return a wrapper for that proc that can be invoked using call syntax (e.g. object:proc(...arguments)). If the object proc calling wrapper is set, calling the returned function will instead call the wrapper proc with the arguments (object, proc, {...arguments}). Note that vars will be shadowed by procs with the same name. To work around this, use the dm.get_var function.

__newindex(index: string, value: any): ()

Set the var specified by index to value, if that var exists on the object.

If the var setting wrapper proc is set, the operation will instead call that proc with the arguments (object, index, value).

Lists

Lists are syntactically similar to tables, with one crucial difference. Unlike tables, numeric indices must be non-zero integers within the bounds of the list.

__index(index: any): any

Read the list at index. This works both for numeric indices and assoc keys. Vars lists cannot be directly read this way if the var getting wrapper proc is set.

__newindex(index: any, value: any): any

Write value to the list at index. This works both for writing numeric indices and assoc keys. Vars lists cannot be directly written this way if the var setting wrapper proc is set.

__len(): integer

Returns the length of the list, similarly to the length builtin in DM.

Iteration

Lists support Luau's generalized iteration. Iteration this way returns pairs of numeric indices and list values. For example, the statement for _, v in L do is logically equivalent to the DM statement for(var/v in L).

Global Fields and Modules

In addition to the full extent of Luau's standard library modules, some extra functions and modules have been added.

Global-Level Fields

sleep(): ()

Yields the active thread, without worrying about passing data into or out of the state.

Threads yielded this way are placed at the end of a queue. Call the awaken hook function from DM to execute the thread at the front of the queue.

loadstring(code: string): function

Luau does not inherently include the loadstring function common to a number of other versions of lua. This is an effective reimplementation of loadstring.

print(...any): ()

Calls the print wrapper with the passed in arguments. Raises an error if no print wrapper is set, as that means there is nothing to print with.

_state_id: integer

The handle to the underlying luau state in the dreamluau binary.

_exec

The _exec module includes volatile fields related to the current execution context.

_next_yield_index: integer

When yielding a thread with coroutine.yield, it will be inserted into an internal table at the first open integer index. This field corresponds to that first open integer index.

_limit: integer?

If set, the execution limit, rounded to the nearest millisecond.

_time: integer

The length of successive time luau code has been executed, including recursive calls to DM and back into luau, rounded to the nearest millisecond.

dm

The dm module includes fields and functions for basic interaction with DM.

world: userdata

A static reference to the DM world.

global_vars: userdata

A static reference that functions like the DM keyword global. This can be indexed to read/write global vars.

global_procs: table

A table that can be indexed by string for functions that wrap global procs.

Due to BYOND limitations, attempting to index an invalid proc returns a function logically equivalent to a no-op.

get_var(object: userdata, var: string): function

Reads the var var on object. This function can be used to get vars that are shadowed by procs declared with the same name.

new(path: string, ...any): userdata

Creates an instance of the object specified by path, with ... as its arguments. If the "new" wrapper is set, that proc will be called instead, with the arguments (path, {...}).

is_valid_ref(ref: any): boolean

Returns true if the value passed in corresponds to a valid reference-counted DM object.

usr: userdata?

Corresponds to the DM var usr.

list

The list module contains wrappers for the builtin list procs, along with several other utility functions for working with lists.

add(list: userdata, ...any): ()

Logically equivalent to the DM statement list.Add(...).

copy(list: userdata, start?: integer, end?: integer): userdata

Logically equivalent to the DM statement list.Copy(start, end).

cut(list: userdata, start?: integer, end?: integer): userdata

Logically equivalent to the DM statement list.Cut(start, end).

find(list: userdata, item: any, start?: integer, end?: integer): integer

Logically equivalent to the DM statement list.Find(item, start, end).

insert(list: userdata, index: integer, ...any): integer

Logically equivalent to the DM statement list.Insert(item, ...).

join(list: userdata, glue: string, start?: integer, end?: integer): string

Logically equivalent to the statement list.Join(glue, start, end).

remove(list: userdata, ...any): integer

Logically equivalent to the DM statement list.Remove(...).

remove_all(list: userdata, ...any): integer

Logically equivalent to the DM statement list.RemoveAll(...).

splice(list: userdata, start?: integer, end?: integer, ...any): ()

Logically equivalent to the DM statement list.Splice(start, end, ...).

swap(list: userdata, index_1: integer, index_2: integer): ()

Logically equivalent to the DM statement list.Swap(index_1, index_2).

to_table(list: userdata, deep?: boolean): table

Creates a table that is a copy of list. If deep is true, to_table will be called on any lists inside that list.

from_table(table: table): userdata

Creates a list that is a copy of table. This is not strictly necessary, as tables are automatically converted to lists when passed back into DM, using the same internal logic as from_table.

filter(list: userdata, path: string): userdata

Returns a copy of list, containing only elements that are objects descended from path.

pointer

The pointer module contains utility functions for interacting with pointers. Keep in mind that passing DM pointers into luau and manipulating them in this way can bypass wrapper procs.

read(pointer: userdata): any

Gets the underlying data the pointer references.

write(pointer: userdata, value: any): ()

Writes value to the underlying data the pointer references.

unwrap(possible_pointer: any): any

If possible_pointer is a pointer, reads it. Otherwise, it is returned as-is.

The SS13 package

The SS13 package contains various helper functions that use code specific to tgstation.

SS13.state

A reference to the state datum (/datum/lua_state) handling this Lua state.

SS13.get_runner_ckey()

The ckey of the user who ran the lua script in the current context. Can be unreliable if accessed after sleeping.

SS13.get_runner_client()

Returns the client of the user who ran the lua script in the current context. Can be unreliable if accessed after sleeping.

SS13.global_proc

A wrapper for the magic string used to tell WrapAdminProcCall to call a global proc. For instance, /datum/callback must be instantiated with SS13.global_proc as its first argument to specify that it will be invoking a global proc. The following example declares a callback which will execute the global proc to_chat:

local callback = SS13.new("/datum/callback", SS13.global_proc, "to_chat", dm.world, "Hello World")

SS13.istype(thing, type)

Equivalent to the DM statement istype(thing, text2path(type)).

SS13.new(type, ...)

An alias for dm.new

SS13.is_valid(datum)

Can be used to determine if the datum passed is not nil, not undefined and not qdel'd all in one. A helper function that allows you to check the validity from only one function. Example usage:

local datum = SS13.new("/datum")
dm.global_procs.qdel(datum)
print(SS13.is_valid(datum)) -- false

local null = nil
print(SS13.is_valid(null)) -- false

local datum = SS13.new("/datum")
print(SS13.is_valid(datum)) -- true

SS13.type(string)

Converts a string into a typepath. Equivalent to doing dm.global_proc("_text2path", "/path/to/type")

SS13.qdel(datum)

Deletes a datum. You shouldn't try to reference it after calling this function. Equivalent to doing dm.global_proc("qdel", datum)

SS13.await(thing_to_call, proc_to_call, ...)

Calls proc_to_call on thing_to_call, with ... as its arguments, and sleeps until that proc returns. Returns two return values - the first is the return value of the proc, and the second is the message of any runtime exception thrown by the called proc. The following example calls and awaits the return of poll_ghost_candidates:

local ghosts, runtime = SS13.await(SS13.global_proc, "poll_ghost_candidates", "Would you like to be considered for something?")

SS13.wait(time, timer)

Waits for a number of seconds specified with the time argument. You can optionally specify a timer subsystem using the timer argument.

Internally, this function creates a timer that will resume the current task after time seconds, then yields the current task by calling coroutine.yield with no arguments and ignores the return values. If the task is prematurely resumed, the timer will be safely deleted.

SS13.register_signal(datum, signal, func)

Registers the Lua function func as a handler for signal on datum.

Like with signal handlers written in DM, Lua signal handlers should not sleep (either by calling sleep or coroutine.yield).

This function returns whether the signal registration was successful.

The following example defines a function which will register a signal that makes target make a honking sound any time it moves:

function honk(target)
	SS13.register_signal(target, "movable_moved", function(source)
		dm.global_procs.playsound(target, "sound/items/bikehorn.ogg", 100, true)
	end)
end

NOTE: if func is an anonymous function declared inside the call to SS13.register_signal, it cannot be referenced in order to unregister that signal with SS13.unregister_signal

SS13.unregister_signal(datum, signal, func)

Unregister a signal previously registered using SS13.register_signal. func must be a function for which a handler for the specified signal has already been registered. If func is nil, all handlers for that signal will be unregistered.

SS13.set_timeout(time, func)

Creates a timer which will execute func after time seconds. func should not expect to be passed any arguments, as it will not be passed any. Unlike SS13.wait, SS13.set_timeout does not yield or sleep the current task, making it suitable for use in signal handlers for SS13.register_signal

The following example will output a message to chat after 5 seconds:

SS13.set_timeout(5, function()
	dm.global_procs.to_chat(dm.world, "Hello World!")
end)

SS13.start_loop(time, amount, func)

Creates a timer which will execute func after time seconds. func should not expect to be passed any arguments, as it will not be passed any. Works exactly the same as SS13.set_timeout except it will loop the timer amount times. If amount is set to -1, it will loop indefinitely. Returns a number value, which represents the timer's id. Can be stopped with SS13.end_loop Returns a number, the timer id, which is needed to stop indefinite timers. The following example will output a message to chat every 5 seconds, repeating 10 times:

SS13.start_loop(5, 10, function()
	dm.global_procs.to_chat(dm.world, "Hello World!")
end)

The following example will output a message to chat every 5 seconds, until SS13.end_loop(timerid) is called:

local timerid = SS13.start_loop(5, -1, function()
	dm.global_proc.to_chat(dm.world, "Hello World!")
end)

SS13.end_loop(id)

Prematurely ends a loop that hasn't ended yet, created with SS13.start_loop. Silently fails if there is no started loop with the specified id. The following example will output a message to chat every 5 seconds and delete it after it has repeated 20 times:

local repeated_amount = 0
-- timerid won't be in the looping function's scope if declared before the function is declared.
local timerid
timerid = SS13.start_loop(5, -1, function()
	dm.global_procs.to_chat(dm.world, "Hello World!")
	repeated_amount += 1
	if repeated_amount >= 20 then
		SS13.end_loop(timerid)
	end
end)

SS13.stop_all_loops()

Stops all current running loops that haven't ended yet. Useful in case you accidentally left a indefinite loop running without storing the id anywhere.