Math Is Fun Forum

Xuer

Member

Registered: 2019-12-23

Posts: 4

LUA how is a function navigating through fields of a table

i already asked this question on stackoverflow and accepted an answer i think i did not really understand the answer and i got some more question, im embarrassed to necro it so im posting it here

im learning lua and got to metatable part, in this example

 local tb = {}
local meta = {}

function tb.new(s)
local super = {}
super.s = s

setmetatable(super,meta)

return super
end

function tb.add(s1,s2)

return s1.s..s2.s

end

meta.__add = tb.add

f= tb.new("W")
t= tb.new("E")

print(f+t)

when compiler gets to

 f = tb.new("W") 

i think this happens

 function tb.new("W")  super.W = W return super end 

so

print(f+t) 

looks like

print(super+super) 

how does

 tb.add(s1,s1) 

find the fields of super table using

 return s1.s..s2.s

also as the

 tb.new

function is called twice and

setmetatable(super,meta) 

happens twice is there any difference between the first and second iteration? if any of the above are incorrect please correct me.

Last edited by Xuer (2021-05-23 03:35:24)

Xuer

Member

Registered: 2019-12-23

Posts: 4

Re: LUA how is a function navigating through fields of a table

i got an answer on another website, so i was under the impression that in this part

super.s = s

the parameter passed to the function

tb.new

replaces both

s=s

turns out it does not and only replaces the rvalue so

 return s1.s...s2.s

works because the index of

 super

is

s

not the value passed to the function  and the table

super

is destroyed upon exit of the

tb.new

function and when it is called again the table is created again, so there are two different versions of the same table.