> What's the reason to concatenate prematurely AND by hand, if it could be done automatically and only if needed? First, it's simplicity (of implementation, ex

> What's the reason to concatenate prematurely AND by hand, if it could be done automatically and only if needed? First, it's simplicity (of implementation, explanation, etc. by far). Second, it depends very significantly on your use case. If your strings are of an average length of 4 bytes (not uncommon, even much shorter in code that does ''.join('<',tag,'>',body,'</',tag,'>') if bodies are short) then you are very likely to take some x4 to x10 memory compared to what you actually need (e.g. if you have allocations and 64-bit pointers). With respect to your socket example, iovecs could be used instead of flattening if you have access to low-level OS primitives, but (a) it would be much slower if the sections are short, and (b) most programming languages and frameworks do not actually give you access to iovec (or equivalent) io calls, for either sockets or files. Ropes have been available since forever in C++, going as far back as the original SGI STL in 1995, RogueWave in 1991 IIRC, and countless other independent implementations. for your typical use case, the complexity (in time and space) that they provide is apparently a net negative. The "s.flatten() before XYZ is idiomatic" is exactly the kind of leaky abstraction that everyone hates, and it requires an understanding that is lacking among most programmers (guaranteeing half the flatten()s will be useless and half of those needed will be missing).