what is the pointer to pointer equivalent in lua

Question

I know that you can use tables in a similar way to pointers in lua. That being said, what would pointers to pointers look like? Would they look something like dp = {p = {}}? if so what would the equivalent to the c code below be in lua?

void InsertItem(node **head, node *newp){
    node **dp = head;

    while((*dp) && (*dp)->value > newp->value
    {
        dp = &(*dp)->next;
    }

    newp->next = *dp;
    *dp = newp;
}

Answer 1

Yes, double pointer may be translated to Lua as nested table.

local function InsertItem(head, newitem)
   while head.next and head.next.value > newitem.value do
      head = head.next
   end
   newitem.next = head.next
   head.next = newitem
end

-- Typical Usage:
local head = {}
InsertItem(head, {value = 3.14})
InsertItem(head, {value = 42})
InsertItem(head, {value = 1})

-- Now the data is the following:
-- head  = {next = elem1}
-- elem1 = {next = elem2, value = 42  }
-- elem2 = {next = elem3, value = 3.14}
-- elem3 = {              value = 1   }