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Comment by unnouinceput | Hacker News Reader

And that's why all modern languages implement streams/string helpers/string builders. You do not want to actually write strings/manipulate them using "+" (concatenation symbol) in code directly because, in modern Unicode world, it tends to become a point of failure for obscure bugs / a maintenance horror show.

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String builders originated in languages with immutable strings making code using something like "foo += bar" in a loop very expensive due to the need to allocate a new string on every iteration. A string builder is basically a mutable string that can be built in-place efficiently and converted to a proper immutable string at the end. It is purely a performance thing, and there are no Unicode issues when concatenating valid Unicode strings (i.e. sequences of codepoints).

Note that some kind of string builders are necessary for efficient repeated concatenation both in languages with immutable strings and in languages with 0-terminated strings.

Using strcat() repeatedly in C for example will mean that the string is being read over and over again to find the end, making an O(n) loop actually O(n²).

Right, but that's still a performance optimization and not anything like what OP is implying.

Yes yes, OP had some really strange ideas. I was just adding some extra info to GP's answer, not trying to contradict them.

I don't understand the link with parent, nor why + would be bad, besides a) because language is naive about concatenation / allocation, and b) if the language allows / doesn't differentiate between a char 'x' and an integer, bc that would result in an integer addition instead of a concatenation.

If you manipulate strings in code using "+" (string concatenation symbol) from a user input you'd be in a world of hurt where you either do a lot of regex (which is ugly and unmaintainable) or you limit the user input to known characters only (which would be a bad user experience and later on your manager would ask you to lift such constraint anyway because they want to support a new feature from now on). Therefore you use, for example, a stream and simply dump your user input in the stream buffer, as they come, and go with that stream in your code from that point on. This way you're future proof too if your manager wants a new feature to support, as example, Chinese and/or Japanese keyboard

Not OP, but I'm still confused. Is this assuming that the language is naive in its implementation of string concatenation so it screws up Unicode?

I'm just not sure what the syntax has to do with the semantics of string concatenation.

I’m even more confused now

Just so you know, Lua's concatenation operator is ".."

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