Function/variable scope (pass by value or reference?)

Question

I\'m completely confused by Lua\'s variable scoping and function argument passing (value or reference).

See the code below:

local a          


        

Answer 1

jA_cOp is correct when he says "all types are passed by value, but function, table, userdata and thread are reference types."

The difference between this and "tables are passed by reference" is important.

In this case it makes no difference,

function modt_1(x)
  x.foo = "bar"
end

Result: both "pass table by reference" and "pass table by value, but table is a reference type" will do the same: x now has its foo field set to "bar".

But for this function it makes a world of difference

function modt_2(x)
  x = {}
end

In this case pass by reference will result in the argument getting changed to the empty table. However in the "pass by value, but its a reference type", a new table will locally be bound to x, and the argument will remain unchanged. If you try this in lua you will find that it is the second (values are references) that occurs.