[pull] develop from nlohmann:develop#129
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`lexer::get()` copied every scanned character into `token_string` on the whole successful-parse hot path, yet that buffer is consumed only by `get_token_string()` when rendering the "last read" fragment of a parse error. On well-formed input the per-byte copy (plus the `unget()` pop) is pure overhead that is always discarded. For seekable input adapters - random-access, single-byte iterators such as those backing `std::string`, `const char*`, and `std::vector<char>` - the offending token is now reconstructed on demand from the input when an error is reported, using a saved start offset, and the eager copy is skipped. Streaming adapters (file, istream, wide-string, and user-defined adapters) keep the eager copy; the strategy is chosen at compile time via `input_adapter_supports_seek`, so adapters without the capability are unaffected. Error messages are byte-for-byte identical across all adapters, verified by a new parity regression test. Microbenchmark (4 MB mixed JSON, parsed from a std::string): ~149 -> ~160 MB/s, about +8%. Signed-off-by: Niels Lohmann <mail@nlohmann.me> Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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