Re: enum/bitops patch

[Asko Kauppi <askok@...>]

...continuing the monologue

Some sample on the usage of the enums -- to give a practical view:


Lua 5.1.1  Copyright (C) 1994-2006 Lua.org, PUC-Rio
> =enum
table: 0x5037c0
> a= enum.new(0x22)
> b= enum.new(0x11,"kuu")

a is an anonymous enum (family ""), b has family "kuu" (Lua in Finnish)

> =b
0x11
> =type(b)
enum    kuu
> =a<b
stdin:1: attempt to compare two enum values
stack traceback:
        stdin:1: in main chunk
        [C]: ?
> c= enum.new(0x44,"kuu")
> =c(b)
false

That was a 'test' operations: binary and with a boolean return - handy.

> =c[b]
0

Binary and, but with numeric return value (0x11 & 0x44 = 0)

> =c("and",b)
0x0

Binary and, with enum (family "kuu") return value; thus 0x0 via  
tostring.

> =c"not"
0xffffffbb
> =c"<<"
0x88

There's numerous call type operations, they all return another enum  
of the same family. These _could_ be done using special (new) Lua  
operations, but don't really (in my opinion) need to be. Also, +,-,*  
etc. arithmetic operations are left undefined for enums. <=  
comparisons are defined, within the family (arguable, but I can think  
of C code that does such - left mainly for ease of porting  
application code).

> =b<c
true

> =a("xor",a,a,a,a,a,a,a)
0x0
> =a("xor",a,a,a,a,a,a,a,a)
0x22

In case there's multiple parameters, they're handled during the same  
call (of course). Also, concatenation is done at bytecode compile  
time (I think), making an effective or:

> print( b..c )
0x55

Concatenation is rather important since it's often used for combining  
flags.

> = a.value
34
> = a"not".value
4294967261

This is the way to get actual numeric values out of the enums  
(tonumber should also work..)

> =tonumber(a)
34
> =tostring(a)
0x22