Re: Per-value metatables would be great for threads

["Christian N." <cn00@...>]

On 2015-08-28 18:35 +0200, Parke wrote:

> As far as numbers with different metatables... that might allow units
> of measure (or other type information) to be associated with numbers.
> I have used that capability in other languages in pursuit of
> correctness and more informative error messages.  For example, is 4
> meters the same as 4 feet?  4 US dollars the same as 4 Euros?

IMHO 4 meters is not the number 4 with additional information, it should 
have its own "meters" type. So if you want the 4 to be different from 
other fours (e.g. not allowing addition with them), wrap in in a table 
or a userdata object and give it the arithmetic metamethods along with 
an appropriate __tostring. If that is too expensive performance-wise, 
then I still think that rather than allowing per-value metatables for 
all value types, a new value type should be introduced for this purpose 
(or a way to create new value-(sub)types on the fly?). The fact that all 
4s are the same is IMHO not (only) a limitation, it also reliefs us from 
much complexity.

(Sorry if that has all already been said, I haven't read all the 
messages about this topic.)


‒ Christian