Re: Why is nil not a valid table key?

[Rici Lake <lua@...>]

On 27-Nov-05, at 12:52 PM, Chris Marrin wrote:

> It is pretty easy to store a 'length' property in a table to identify 
> how many numeric keys it has.

Sure. I think Mike was talking about the general iteration case, 
though, not the numeric one.

>  I found that technique ALMOST works in Lua. If a table has entries 
> for numeric keys 1,2,12 and 17, and I set the length property to 17 
> then I can go:
>
>     for i=1,t.length do
>         print(t[i])
>     end
>
> and I will get all the numbers printing out, with nils in the slots 
> that don't have a numeric index.

In fact, that's the way it was at one time (with 'n' in place of 
'length').

> But I found that attempting to set:
>
>     t[0] = "hello"
>
> does not work. When I read this back, it prints nil. Is this true, or 
> do I have a bug in my logic somewhere?

You have a bug in your logic somewhere.

Lua 5.1 (beta)  Copyright (C) 1994-2005 Lua.org, PUC-Rio
> t = {}
> t[0] = "Hello"
> =t[0]
Hello

Lua 5.0.2  Copyright (C) 1994-2004 Tecgraf, PUC-Rio
> t = {}
> t[0] = "Hello"
> =t[0]
Hello