Scripting with Lua - Game Coding Complete - page 345

you are using the map section. This is done mostly for optimization reasons, as Lua
uses a true array for the array section and a hash map for everything else. This typi-
cally only comes into play when you want to loop through all the elements of a table,
which you ' ll see below. Note that all tables have these sections, so there ' s nothing

stopping you from using both in a single table.
In the first example, a table was initialized with the first five prime numbers. You can
also initialize tables that use non-integer keys by wrapping the key in square brackets
and using the assignment operator. The messy table above could be created like this,
assuming that anotherTable and X were already defined:

messyTable = { [“string”] = 20, [“another string”]=“data”,
[anotherTable] = 5, [X] = anotherTable }
You can actually do both:

temp = { [ “ hat ” ]= “ blue ” ,5, “ purple ” ,[ “ ninja ” ]=3}

This is equivalent to:

temp = {}
temp[ “ hat ” ]= “ blue ”

temp[1] = 5
temp[2] = “ purple ”

temp[ ]=3

Indexing a table by string is so common that Lua provides a bit of syntax sugar to
make it a little cleaner. First, you don

“ ninja ”

t have to surround string keys with square
brackets or quotes when initializing the table. Second, you can access the value by
using the

'

operator with no quotes. These two tables are identical, and the two
print statements show two different ways to access them:

“ . ”

v1={[ “ x ” ] = 13.5, [ “ y ” ]=1,[ “ z ” ] = 15.4 }

v2 = { x = 13.5, y = 1, z = 15.4 }
print(v1[ “ x ” ]) -- > prints 13.5

print(v1.x) > prints 13.5

v1.y = 3 -- you can set values using the

-

' . ' operator as well

Lua provides a special table named “ table ” that contains a number of helper functions

for table manipulation. I m not going to go into detail on these functions, since you

can look them up pretty easily, but here ' s the one-line description for each:

'

n insert() : Inserts elements into the table.
n remove() : Removes elements from the table.
n getn() : Returns the number of elements in the array section of the table (not
including the map section).