[BeeOnRope]

Note that this is directly contradicted by another commnent[1] on this post, where three fixed strings are concatenated with +=, yet that was still slower.

Perhaps the use of += as separate statements is the difference, but one would hope that gc wasn't so fragile as to be unable to identify those sequences as identical.

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[1] https://news.ycombinator.com/item?id=16533650

[tapirl]

The optimization made by gc is only valid for the form: s0 + s1 + .... + sn.

[lugg]

I suspect / understood that as being the optimization is based on the fact that those are concatenated references and not string literals.

I don't quite understand why string literals wouldn't be even easier to optimize but there it is.