Mindex Metamethod

The __mindex metamethod stands for 'method index'. It has a secondary priority to __index and it's only invoked when the lookup is being performed by method invocation syntax. This is used to avoid compatibility issues regarding Pluto's default metatable for tables. For example:

pluto
local t = { "a", "b", "c" }
print(t:concat()) --> abc

In this code, the following occurs:

1. concat key is not directly present in the table, so __index is queried.
2. __index returns nil.
3. Since __index returned nil and this lookup is being performed by method invocation syntax (:), __mindex is queried.

An example showing how __mindex is walked recursively so :insert still works with a custom __mindex
pluto
local t = setmetatable({}, {
    __mindex = {
        function sum()
            local accum = 0
            for self as v do
                accum += v
            end
            return accum
        end
    }
})
t:insert(1)
t:insert(2)
print(t.sum) --> nil
print(t:sum()) --> 3

An example of a field taking precedence
pluto
local t = { 1, 2 }
print(t:min()) --> 1
t.min = 1
print(t:min()) -- attempt to call a number value