Table is being changed, outside of its lua file

Getting Started Newbie Questions
1

Good day, I was wondering why is my table being altered even though I set it as a use of reference for other table. Sample:

tableCopy.lua

local M = {} local origTable = loadTableFromJson M.copyTable = function() local otherTable = origTable return otherTable end return M

main.lua

local tableCopy = require("tableCopy") local myTable = {} myTable = tableCopy.copyTable() myTable.hp = myTable.hp - 1 -- Output is from 10 to 9 local newTable = tableCopy.copyTable() newTable.hp = newTable.hp - 1 -- Output is 8, the hp still retains

as you can see, the hp still continues even though, in my copyTable.lua I’m just copying the table. I already solved it by just reReading the JSON again, just asking why does this happen?

thanks in advance

2

When you assign otherTable = origTable, you aren’t making a copy. You are storing a reference to the table named ‘origTable’ in otherTable.

You need a function which creates a brand new object with the same properties as the old.

https://forums.coronalabs.com/topic/27482-copy-not-direct-reference-of-table/

Depending on the size and complexity of your table, this can be a fairly slow process. It might be quicker to just re-read the data.

3

okay thanks, i already did the re-read the data. I was wondering what was happening, thank you

4

Don’t reload the JSON.  That is slow and if you do it a lot it will affect the game performance as well as burn battery life.

Make a copy of the table.

If you have SSK2, it has several copy features: 

  • table.shallowCopy() - Create new table copying first level of source table.  Copies of sub-levels are references.
  • table.shallowStripCopy() - Same, but do not copy functions or userdata (in preparation for serialization).
  • table.deepCopy() - Traverse entire table and create complete copy of all data.  Cannot handle cyclic tables.
  • table.deepStripCopy() - Same, but with serialization prep.

Note: You can also find table copying examples by searching for “Lua Table Copy”  here is one example (Rosetta Code is one of my favorite sites):

https://rosettacode.org/wiki/Deepcopy#Lua

5

When you assign otherTable = origTable, you aren’t making a copy. You are storing a reference to the table named ‘origTable’ in otherTable.

You need a function which creates a brand new object with the same properties as the old.

https://forums.coronalabs.com/topic/27482-copy-not-direct-reference-of-table/

Depending on the size and complexity of your table, this can be a fairly slow process. It might be quicker to just re-read the data.

6

okay thanks, i already did the re-read the data. I was wondering what was happening, thank you

7

Don’t reload the JSON.  That is slow and if you do it a lot it will affect the game performance as well as burn battery life.

Make a copy of the table.

If you have SSK2, it has several copy features: 

  • table.shallowCopy() - Create new table copying first level of source table.  Copies of sub-levels are references.
  • table.shallowStripCopy() - Same, but do not copy functions or userdata (in preparation for serialization).
  • table.deepCopy() - Traverse entire table and create complete copy of all data.  Cannot handle cyclic tables.
  • table.deepStripCopy() - Same, but with serialization prep.

Note: You can also find table copying examples by searching for “Lua Table Copy”  here is one example (Rosetta Code is one of my favorite sites):

https://rosettacode.org/wiki/Deepcopy#Lua