Using a table as a function argument

This is a design pattern in Lua to make it possible to add parameters to a function without needing to break backwards compatibility with older code.

Say we make a first version of a function and it takes one parameter like this:

function FOO(T)
   local Data = T.data
end

Then to call this function we have:

FOO{data="MYDATA"}

Then we realize that we need a timeout, we can extend the function to support a second parameter without needing to alter previous code calling this function. In fact, we can code things in a way that adds a default.

function FOO(T)
   local Data = T.data
   local Timeout = T.timeout or 1000;  --This parameter defaults to 1000 if not present
end

So now our old code still works, but newer code can optionally pass in the new parameter:

In fact the pattern allows us to remove parameters which are no longer needed and still not break old code that might be using those unneeded parameters:

Contrast if we had written FOO this way: