Re: predefined constants

[David Jones <drj@...>]

On Jul 24, 2004, at 09:55, Adrian Sietsma wrote:

> I am looking at cutting an existing c++ algorithm to lua.
> The current c++ version uses a lot (~30) of #defined state flags.
>
> my lua options seem to be
> 1/ just use integer constants
> if s == 1 then ...... elseif s==2 then ... end
> should be fastest, but hardest to read.
>
> 2/ use local vars
> local STATE_1, STATE_2, STATE_3 = 1,2,3
> if s == STATE_1 then ... end
>
> this reads nicely, but all those locals are a pain, and i don't really 
> need variables - the states are just symbols
>
> 3/ use strings
> if s == "STATE_1" then ...... end
>
> still reads nicely, but are all those string comparisons going to cost 
> much ?

String equality (s == "STATE_1") is very fast as strings are hashed 
(interned) and this test is just a pointer comparison.  I'd go with 
strings.

> any other suggestions ?
>
> i don't like the #define approach, but could lua do with a "const" 
> keyword, for immutable data (symbolic constants)? this would 
> presumably be translated to the literal value during compile.
> eg
> const STATE_1 = 1
> if (s == STATE_1) then...
>
> would compile to
> if (s == 1) then...
>
> feel free to tell me that is impossible / a bad idea because.. / 
> doesn't match the LUA design philosophy / etc.

It comes up a lot on the list, you search the archives if you feel like 
discussing it.

Cheers,
 drj