Metatable Index

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#1

According to the wiki, the metamethod “__index” fires when an index in a table is read from if the value for that index is nil.

I don’t quite understand what “table” they mean. For example:

local mt = {"ya"}
mt.__index = mt

local t = {}
setmetatable(t,mt)
print(t[1])

According to their explanation, the “table” is “t”, correct? If that’s true, i’m guessing that “mt” being a metatable of “t” has something to do with mt’s metamethod __index being fired when t[1] is tried (t[1] is nil).

Can someone please clarify.

#2

Think of a metatable as a table of events that occur when certain operations happen in relation to a table.
You can actually make a single table both a metatable and table. But in that instance yes mt is the table where you can intervene in operations that occur with table t.

#3

Everything you stated is correct.

When you do t[1]:

  1. Lua checks it t[1] exists. If so, Lua returns it.
  2. Lua checks if t has a metatable (mt). If not, Lua returns nil.
  3. Lua checks if mt has an __index. If not, Lua returns nil.
  4. Lua checks if __index is a table. If so, Lua returns __index[1].
  5. Lua checks if __index is a function. If so, Lua returns __index(t, 1).

Your example will print "ya" because it hits step 4.

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#5

a good way to use it would be to store functions and etc that multiple objects of that class would use