Nested Tables

A value in a table can be another table, and that one can hold more tables. That's how you describe something bigger, like the whole farm:

local farm = {
    name = "Sunflower Farm",
    coins = 120,
    barn = {eggs = 18, milk = 6},
    fields = {"carrot", "potato", "pumpkin"},
}

print(farm.barn.eggs)
print(farm.fields[2])
print(#farm.fields)

This prints:

18
potato
3

Read farm.barn.eggs from left to right: farm.barn is the barn's table, and .eggs reads the key eggs from it. You can chain dots and square brackets as far as you need: farm.fields[2] is the second item of the list in the field fields. Changing a value works the same way: farm.barn.eggs = farm.barn.eggs + 6.

The inner tables can be dictionaries, lists or records, mixed as you like. Here is a dictionary of records, one for each animal:

local animals = {
    bella = {kind = "cow", age = 4},
    rex = {kind = "dog", age = 2},
}

print(animals.bella.kind .. ", " .. animals.bella.age .. " years old")
print(animals.rex.kind)

cow, 4 years old
dog

Lists can be nested too: a field of plots, row by row, is a list of lists, and plots[2][3] is the third plot in the second row.

The typical mistake is reading through a table that isn't there. Say Emma keeps her tools in a shed, but the farm has no shed yet:

local farm = {name = "Sunflower Farm", barn = {eggs = 18}}

print(farm.shed.tools)

main.lua:3: attempt to index a nil value (field 'shed')

To index a table means to get to one of its keys, with a dot or square brackets. farm.shed is nil, and you can't read the key tools from nil. The message names the field that was nil, 'shed': the problem is the part before the last dot, not tools. You get the same error when you assign, farm.shed.tools = 4: Lua doesn't create the inner table for you. Create it first:

local farm = {name = "Sunflower Farm", barn = {eggs = 18}}

farm.shed = {}
farm.shed.tools = 4
print(farm.shed.tools)

4

Or in one step: farm.shed = {tools = 4}. When you aren't sure that an inner table is there, check first: if farm.shed then … end, or in one expression, farm.shed and farm.shed.tools, which is nil instead of an error when there's no shed.