Question

I am starting to learn Lua from Programming in Lua (2nd edition)
I didn’t understand the following in the book. Its very vaguely explained.

a.) w={x=0,y=0,label="console"}

b.) x={math.sin(0),math.sin(1),math.sin(2)}

c.) w[1]="another field"

d.) x.f=w

e.) print (w["x"])

f.) print (w[1])

g.) print x.f[1]

When I do print(w[1]) after a.), why doesn’t it print x=0

What does c.) do?

What is the difference between e.) and print (w.x)?

What is the role of b.) and g.)?

Answer 1

You have to realize that this:

t = {3, 4, "eggplant"}

is the same as this:

t = {}
t[1] = 3
t[2] = 4
t[3] = "eggplant"

And that this:

t = {x = 0, y = 2}

is the same as this:

t = {}
t["x"] = 0
t["y"] = 2

Or this:

t = {}
t.x = 0
t.y = 2

In Lua, tables are not just lists, they are associative arrays.

When you print w[1], then what really matters is line c.) In fact, w[1] is not defined at all until line c.).

There is no difference between e.) and print (w.x).

b.) creates a new table named x which is separate from w.

d.) places a reference to w inside of x. (NOTE: It does not actually make a copy of w, just a reference. If you’ve ever worked with pointers, it’s similar.)

g.) Can be broken up in two parts. First we get x.f which is just another way to refer to w because of line d.). Then we look up the first element of that table, which is "another field" because of line c.)