Re: Exposure of nil to end-users

[steve donovan <steve.j.donovan@...>]

This is the famous 'nullable type' problem.

One option is for the database layer never to return nil in the case
of a NULL field, but "" or 0 depending on the type of the field.

Another option is to make a special Null object which has default
string-like and number-like semantics. But this is tricky to do
properly, since you'd need to define methods like 'null:sub(1,1)' etc
as well as override __concat, __add, etc.

steve d.

On Thu, Feb 5, 2009 at 12:05 PM, Ben Harper <rogojin@gmail.com> wrote:
> I am using Lua as a language that allows end-users to manipulate
> database records.
> My problem is that I'm not sure how to expose NULL values to the user.
>
> In this example, value = nil
> User Types:      value .. "abc"
> User Expects:   'abc'
> User Gets:        Error: attempt to concatenate a nil value
>
> Has anybody had a similar problem, and how have you dealt with it?
>
> Thanks,
> Ben
>