string.sub for suffix not usable with varying length (including zero)
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- Subject: string.sub for suffix not usable with varying length (including zero)
- From: Richter, Jörg <Joerg.Richter@...>
- Date: 2013年2月11日 10:26:31 +0000
Consider this function:
local function cut( str, prelen, postlen )
return str:sub(1,prelen)..str:sub(-postlen)
end
print( cut( "abc", 1, 1 ) ) -- "ac"
print( cut( "abc", 0, 1 ) ) -- "c"
print( cut( "abc", 1, 0 ) ) -- "aabc"
This function uses the canonical way to extract a prefix and postfix
of a string. But I think the third result is a little bit surprising.
Seems like in Lua 5.1 it was undefined what string.sub( str, 0 ) does.
Lua 5.2 has one more paragraph describing what happens in this case.
But I think this paragraph was only added for cases like this:
string.sub( "abc", -4 )
Currently I have to special case the above function for postlen==0.
Or I have to use positive indexes.
string.sub( str, #str-postlen+1 )
But this is not very pretty.
Is it possible to change this?
Jörg