Scripting with Lua - Game Coding Complete - page 344

Lua Tables Are 1-Indexed!

If you s a typo in the above code

sample. Surely prime[2] should point to 5, right? Not in Lua! Lua is 1-
indexed, meaning that all arrays start at the index of 1, as opposed to C++,
which is 0-indexed. I guarantee that this rather unfortunate decision by the
developers of Lua will cause bugs in your code. This becomes especially messy
when you pass array indexes between C++ and Lua.

' re paying attention, you might think there '

'

It s important to note that in the above example, prime is just a reference to the real

table object. If you assign prime to another variable, Lua does a simple pointer copy,
and both variables will contain references to the same table.

prime = { 2, 3, 5, 7, 11 } -- the original table
prime2 = prime -- this is just a simple pointer copy
print(prime, prime2) -- > this prints out “ table: 02D76278 table: 02D76278 ”

prime2[1] = 10
print(prime[1]) -- > prints out “ 10 ”

Tables don s just the default. You can

index tables using anything, including numbers, strings, other tables, functions, or
anything else you want.

' t have to be indexed using a number, that '

messyTable = {} -- an empty table

-- index by string
messyTable[ “ string ” ]=20

messyTable[ “ another string ” ]= “ data ” -- the data doesn t have to

-- be consistent either

'

-- index by table
anotherTable = {}
messyTable[anotherTable] = 5

-- index by function
Function X() end
messyTable[X] = anotherTable -- this time the data is another table

As you can see, tables have the ability to get very messy. In practice, you probably
wouldn ' t have a table that was so inconsistent with its keys and data. One interesting
property of Lua tables is that they treat integer-indexed items separately from every-
thing else. Under the covers, tables actually have two sections. One section behaves
like a resizable array and the other like a map. As the programmer, you rarely have to
worry about the differences between these. When you create a table like the prime
table above, you are using the array section. When you create one like messyTable ,