Lua 5.3.0-work2: utf8.sub?
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- Subject: Lua 5.3.0-work2: utf8.sub?
- From: Dirk Laurie <dirk.laurie@...>
- Date: 2014年4月11日 07:59:53 +0200
There's no utf8.sub. Anyone tried to code it in pure Lua yet?
This is my attempt:
function utf8.sub(s,i,j)
i = i or 1
j = j or -1
if i<1 or j<1 then
local n = utf8.len(s)
if not n then return nil end
if i<0 then i = n+1+i end
if j<0 then j = n+1+j end
if i<0 then i = 1 elseif i>n then i = n end
if j<0 then j = 1 elseif j>n then j = n end
end
if j<i then return "" end
i = utf8.offset(s,i)
j = utf8.offset(s,j+1)
if i and j then return s:sub(i,j-1)
elseif i then return s:sub(i)
else return ""
end
end
Notes:
1. Care is taken to avoid calculating utf8.len(s) when it is not necessary.
2. The use of utf8.offset implies that the result is undefined when s is not
a valid UTF8 sequence.
This code is _long_. Sure would be nice if the utf8 library already had that :-)