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.
