LUA indexed table access via named constants - lua

Question

I am using LUA as embedded language on a µC project, so the ressources are limited. To save some cycles and memory I do always only indexed based table access (table[1]) instead og hash-based access (table.someMeaning = 1). This saves a lot of memory.
The clear drawback of this is approach are the magic numbers thrughtout the code.
A Cpp-like preprocessor would help here to replace the number with named-constants.
Is there a good way to achieve this?
A preprocessor in LUA itself, loading the script and editing the chunk and then loading it would be a variant, but I think this exhausts the ressources in the first place ...

Answer 1

So, I found a simple solution: write your own preprocessor in Lua!
It's probably the most easy thing to do.
First, define your symbols globally:
MySymbols = {
FIELD_1 = 1,
FIELD_2 = 2,
FIELD_3 = 3,
}
Then you write your preprocessing function, which basically just replace the strings from MySymbols by their value.
function Preprocess (FilenameIn, FilenameOut)
local FileIn = io.open(FilenameIn, "r")
local FileString = FileIn:read("*a")
for Name, Value in pairs(MySymbols) do
FileString = FileString:gsub(Name, Value)
end
FileIn:close()
local FileOut = io.open(FilenameOut, "w")
FileOut:write(FileString)
FileOut:close()
end
Then, if you try with this input file test.txt:
TEST FIELD_1
TEST FIELD_2
TEST FIELD_3
And call the following function:
Preprocess("test.txt", "test-out.lua")
You will get the fantastic output file:
TEST 1
TEST 2
TEST 3
I let you the joy to integrate it with your scripts/toolchain.
If you want to avoid attributing the number manually, you could just add a wonderful closure:
function MakeCounter ()
local Count = 0
return function ()
Count = Count + 1
return Count
end
end
NewField = MakeCounter()
MySymbols = {
FIELD_1 = NewField(),
FIELD_2 = NewField(),
FIELD_3 = NewField()
}