https://issues.dlang.org/show_bug.cgi?id=13877
--- Comment #5 from [email protected] --- Commits pushed to master at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/f81de7d9b9a9d4d8af4615306b2b759f845bd792 Fix Issue 13877 - join assumes forward range can be cheaply iterated twice e.g. with `r.map!(someExpensiveFunction).join`, `join` would previously iterate twice: once to compute length, and again to build up the result. The extra iteration to compute length may be disproportionately expensive, so we now only precompute length for built-in arrays, since we know those are cheap to iterate. The heuristic could be improved over time, although I can't think of anything better right now. https://issues.dlang.org/show_bug.cgi?id=13877 https://github.com/D-Programming-Language/phobos/commit/ba100ff803f8d266f97e9c02503e19f961be1e7e Merge pull request #2837 from Poita/Issue13877 Fix Issue 13877 - join assumes forward range can be cheaply iterated twice --
