How do you duplicate a variable's value without using the same memory address?
I thought I understood how a variable worked with a variable being assigned an address in memory where you can store a value, though evidently I don't. I have this small snippet of code here that finds certain combination of numbers that fit into a bigger number. My issue is where if result == 0 then I try to copy the value of priorPath to a different variable completedPath, then add list[i] into the table completedPath, and then store completedPath into another table storing all possible paths. My issue is that any changes to completedPath all show up on priorPath which I don't want to happen. So back to the original question, how do I declare a variable of equal value using a different memory address?
local function testNumber(number, exit)
if number > exit then return false end
return exit - number
end
local function getPaths(list, goal, priorPath, paths)
--print(goal)
for i = 1, #list do
local result = testNumber(list[i], goal)
if result == 0 then
local completedPath = priorPath
table.insert(completedPath, list[i])
table.insert(paths, completedPath)
elseif result then
table.insert(priorPath, list[i])
paths = getPaths(list, goal - list[i], priorPath, paths)
end
end
return paths
end
Edit: I ended up having to do something stupid like the following, and it worked, any better solutions?
local function testNumber(number, exit)
if number > exit then return false end
return exit - number
end
local function getPaths(list, goal, priorPath, paths)
for i = 1, #list do
print(list[i])
local result = testNumber(list[i], goal)
if result == 0 then
local newTbl = {}
for k,l in pairs(priorPath) do
table.insert(newTbl, l)
end
table.insert(newTbl, list[i].." ")
table.insert(paths, newTbl)
elseif result then
local newTbl = {}
for k,l in pairs(priorPath) do
table.insert(newTbl, l)
end
table.insert(newTbl, list[i])
paths = getPaths(list, goal - list[i], newTbl, paths)
end
end
return paths
end
1 answer
This happens because userdata and table data types are pass-by-reference, while numbers, strings and other data types are pass-by-value. This means that, as you have found, creating new variables will still refer to the same copy of the table. To solve this, there are two options that I know of:
In the case of predetermined tables (for example, a table containing default stats), you can create and return the table from a function to obtain a unique copy of the table every time. For example:
local function GetStats()
return {
Money = 5;
Level = 0
}
end
local Stats1 = GetStats()
local Stats2 = GetStats()
print(Stats1 == Stats2) --> false
Alternatively, if your table is created/altered while the game is running (in most cases), you can make a function to create a unique copy of the table:
local function DeepCopy(Table)
local Copy = {}
for Key, Value in pairs(Table) do
if type(Value) == "table" then
Copy[Key] = DeepCopy(Value)
else
Copy[Key] = Value
end
end
return Copy
end
local Table1 = {"a", "b", "c"}
local Table2 = DeepCopy(Table1)
print(Table1 == Table2) --> false
Hope this helps!
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