CODEWITHSUNDEEP
indexingluametatablemeta-method
Vinni Marcon
Vinni Marcon

Reputation: 616

how to make then __index and __newindex detect table.index

I'm still a little newbie with metatables, and there is something that makes me confused

when I use metamethods like __index and __newindex in my metatable, they are only called when I invoke an element of the table as follows:

print(table[index]) -- this call the __index

table[index] = value -- this call the __newindex

but these two metamethods are not called when I invoke an element of the table as follows:

print(table.index) -- this does NOT call __index

table.index = value -- this does NOT call __newindex

my question is, is there any way to make table.index also call these two metamethods? or does only table[index] work?

Upvotes: 0

Views: 1144

Answers (2)

2dengine
2dengine

Reputation: 89

Yes, __index will work with both brackets: mytable["index"] as well as the dot operator: mytable.index

mytable = setmetatable({}, { __index = function(t, k)
  if k == "index" then
    return "works fine"
  end
  return rawget(t, k)
end })

print(mytable["index"])
print(mytable.index)

You can circumvent the preset metatable methods using rawget and rawset

Having said that, if you are new to Lua I recommend looking for simple solutions that work WITHOUT metatables.

Upvotes: 2

DarkWiiPlayer
DarkWiiPlayer

Reputation: 7046

the __idnex and __newindex metamethods only get used when the table doesn't have an element at the index in question. If there's already an element, indexing will just return that element and setting it will just overwrite the existing element.

If you want complete control over all indices in a table, you have to keep it 100% empty and save all its values in another table and access those using the metamethods.

Upvotes: 1

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