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Niels Lohmann
8220c48141
Before C++20, a pair of iterators of a contiguous container cannot be told from any other random-access iterator, so json::parse(s.begin(), s.end()) on a std::string or std::vector<char> was read one character at a time, without the bulk scans of strings, numbers and indentation that the container itself gets (the container overload of input_adapter() already maps it to a pointer range). The iterators of std::string and of a std::vector of 1-byte integral elements are now matched exactly and mapped to the pointer range they cover; an empty range is not dereferenced. The character type stays the same, so the results and error positions do not change. parse(first, last) of a std::string gets 1.7-2.0x as fast in C++17 on an Apple M1 Max, accept(first, last) 2.7-3.1x, and from_cbor(first, last) of a std::vector 8-23% faster. Signed-off-by: Niels Lohmann <mail@nlohmann.me>