LuaWML/Variables

This page describes the LuaWML functions and helpers for handling WML variables and containers.

wesnoth.get_variable

Loads a WML variable with the given qualified name (argument 1) and converts it into a Lua object. Returns nil if the name does not point to anything, a scalar for a WML attribute, and a table for a WML object. The format of the table is described in LuaWML#Encoding WML objects into Lua tables.

wesnoth.fire("store_unit", { variable="my_unit", { "filter", { id="hero" } } })
local heros_hp = wesnoth.get_variable("my_unit[0].hitpoints")
wesnoth.message(string.format("The 'hero' unit has %d hitpoints.", heros_hp))

Argument 2, if true, prevents the recursive conversion when the name points to an object; a fresh empty table is returned in this case. This is mainly used for writing proxy objects, e.g. in #helper.set_wml_var_metatable.

Note that, if the variable name happens to designate a sequence of WML objects, only the first one (index 0) is fetched. If all the WML objects with this name should have been returned, use #helper.get_variable_array instead.

wesnoth.set_variable

Converts and stores a Lua object (argument 2) to a WML variable (argument 1). A WML object is created for a table, an attribute otherwise.

wesnoth.set_variable("my_unit.hitpoints", heros_hp + 10)

Setting a WML variable to nil erases it.

helper.set_wml_var_metatable

Sets the metable of a table so that it can be used to access WML variables. Returns the table. The fields of the tables are then proxies to the WML objects with the same names; reading/writing to them will directly access the WML variables.

helper.set_wml_var_metatable(_G)
my_persistent_variable = 42

helper.get_child

Returns the first sub-tag of a WML object with the given name.

local u = wesnoth.get_units({ id = "Delfador" })[1]
local costs = helper.get_child(u.__cfg, "movement_costs")
wesnoth.message(string.format("Delfador needs %d points to move through a forest.", costs.forest))

If a third parameter is passed, only children having a id attribute equal to it are considered.

helper.child_range

Returns an iterator over all the sub-tags of a WML object with the given name.

local u = wesnoth.get_units({ id = "Delfador" })[1]
for att in helper.child_range(u.__cfg, "attack") do
    wesnoth.message(tostring(att.description))
end

helper.get_variable_array

Fetches all the WML container variables with given name and returns a table containing them (starting at index 1).

function get_recall_list(side)
    wesnoth.fire("store_unit", { x = "recall", variable = "LUA_recall_list })
    local l = get_variable_array "LUA_recall_list"
    wesnoth.set_variable "LUA_recall_list"
    return l
end

helper.get_variable_proxy_array

Creates proxies for all the WML container variables with given name and returns a table containing them (starting at index 1). This function is similar to #helper.get_variable_array, except that the proxies can be used for modifying WML containers.

helper.set_variable_array

Creates WML container variables with given name from given table.

helper.set_variable_array("target", { t1, t2, t3 })
-- target[0] <- t1; target[1] <- t2; target[2] <- t3