Application of indexing to all types

[Doug Rogers <rogers@...>]

I've been thinking, which isn't a good sign...

On another thread I mentioned that I liked the colon notation and wished 
that it could be applied to all types; PA disagreed, using dental care 
for his reasoning. :)

Mike Pall pointed me to the code that handles it along with a suggestion 
on how to make it work. I will probably play around with it at some 
point (I'm already spending time away from work I *should* be doing!). 
For now I just want to discuss it.

I think it would be nice to extend the use of '.' and ':' to all types. 
I'd like to be able to do something like this:

> s='abcd'
> s:print()
abcd
> print(s:len())
4
> c=coroutine.create(function() print('hey!') end)
> c:resume()
hey!
> n=6
> n:print()
6
>

The last one doesn't help much but I think the other two help with 
readability - and typing.

I was thinking that each non-table, non-nil type - 'number', 'string', 
'thread', 'boolean' - would have its own table with a metatable attached 
with __index set to that table. This would allow the VM to easily (and 
quickly) push the table associated with the type onto the stack before 
attempting to index a non-table type. 'nil' would still result in an error.

In the examples above, the ones that are of the form x:print() would 
require the use of the global table if the type table did not resolve 
the name. I'm not so worried about supporting that as I am about things 
like s:len() mapping to string.len(s). In the 'print' case it may be 
better for an error to be raised. A developer could always set 
string.print = print and the system above would work.

I like the idea, and I'm wondering what others think. Am I the only one 
who loves the colon notation and wishes that it applied to all the 
built-in types?

By the way, why do we call the library 'coroutine' and the type 
'thread', but with string we use 'string' and 'string'? I suspect it is 
to avoid the name space collisions for 'thread' but to keep the type 
name shorter than 'coroutine'. Of course the name space argument could 
certainly be used for 'string'. Unfortunate, since it makes this idea 
harder to implement.

Thanks to the creators of Lua. It is a thing of beauty, even with these 
little 'flaws'. :)

Doug

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Doug Rogers - ICI - V:703.893.2007x220 www.innocon.com
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