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- Subject: Re: lists with nil play nice for Lua 5.2
- From: Adrien de Croy <adrien@...>
- Date: Fri, 10 Aug 2007 13:51:43 +1200
actually this does cause a bit of confusion.
We've got an interface that allows people to manipulate data in a DNS
packet which is housed in a C++ object.
since DNS packets can have numerous records in them, there needs to be a
way to index them.
Doing this from Lua then becomes confusing, since accessing the C++
object from Lua uses 0-based indexing, but accessing any other normal
array/table in lua uses 1-based indexing. I'm not looking forward to
explaining that to users.
Our policy control system has a script-based option, which calls a Lua
function which returns a bool. The user can fill out the body of the
function, so we have the situation like
if (Request.Query.Name == "www.microsoft.com") then
Request.Query.Name = "www.wingate.com";
Since we have __index metamethod on the table represented as "Request",
we get a callback with a name and offset which we can resolve.
I guess we could just subtract 1 from the index number passed up and use
"native" lua indexing ....
I do agree that when you are specifying a for loop with a sequence
defined as "1,N" then it makes a lot more sense to have "1,N" rather
It's more a function of how the syntax of the for loop works which then
passes over to table indexing.
John Belmonte wrote:
Jerome Vuarand wrote:
In this paper he says that 0-based indexing is better if you use
convention 'a' (loops of the form 'for (i=0; i<N; ++i)'). Lua uses
convention 'c' (loops of the form 'for (i=1; i<=N; ++i)', or in Lua 'for
i=1,N do'), so 1-based indexing is more suited to Lua.
That is a recursive argument. Lua uses convention "c" because it has
1-based indexing. The choice of index base drives how you specify
ranges. No sane language or library would mix 1-based indexing with
half-open ranges, or 0-based indexing with closed ranges.
Adrien de Croy - WinGate Proxy Server - http://www.wingate.com