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• Subject: Re: string like arrays
• From: Marco Antonio Abreu <falecomigo@...>
• Date: Wed, 16 Jan 2008 22:22:33 -0200

```Thanks everyone,

```
I already tried something like this, but it introduces more code in the middle reducing performance. About to write, I thought the answer will be this one (immutable).
```
Anyway, thank you a lot.

Marco Antonio Abreu
falecomigo@marcoabreu.eti.br
http://www.marcoabreu.eti.br

Luis Carvalho wrote:
```
there is some how, in Lua, to access string bytes like an array; something like what we can use in C or Pascal?
```
examples:

s = 'Lua race'
print( a[5] ) --> prints "r"

It would be very desirable to be able to write too, like:

s[5] = 'f'
print( s ) --> prints "Lua face"
```
```
Not with Lua strings since they're immutable. But you can roll something like:

function mutstring (s)
assert(type(s) == "string", "string expected")
local ms = s or ""
local u = newproxy(true)
local mt = getmetatable(u)
local relatpos = function(p)
local l = #ms
if p < 0 then p = l + p + 1 end
if p < 1 then p = 1 end
return p, l
end
mt.__index = function(_, k)
assert(type(k) == "number", "number expected as key")
local k, l = relatpos(k)
if k <= l then
return ms:sub(k, k)
end
end
mt.__newindex = function(_, k, v)
assert(type(k) == "number", "number expected as key")
assert(type(v) == "string" and #v == 1, "character expected as value")
local k, l = relatpos(k)
if k <= l + 1 then
ms = ms:sub(1, k - 1) .. v .. ms:sub(k + 1, l)
end
end
mt.__len = function(_) return #ms end
mt.__tostring = function(_) return ms end
return u
end

Test:

```
```s = mutstring("Lua race")
print(s[5])
```
```r
```
```s[5] = "f"
print(s)
```
```Lua face

Cheers,
Luis.

```
```
```