Niels LohmannandClaude 78e2a87ab1 Require a container's value_type to match what data() points at ...

is_contiguous_byte_container accepted any type with a data() returning a
pointer to a single-byte integral plus a size(). That is duck typing: the two
members say nothing about size() counting the units data() points at.

A type where it does not - fixed-size records, say - was routed to the
pointer-based adapter and parsed as [data(), data() + size()) bytes, silently
truncating input the iterator-based adapter had read in full:

    struct record_buffer {
        using value_type = std::array<char, 4>;
        std::string bytes;
        const char* data() const;                        // raw bytes
        std::size_t size() const;                        // in records
        const char* begin() const; const char* end() const;
    };
    json::parse(record_buffer{"[1,2,3,4,5]"});           // parse error at column 3

Requiring the container's own value_type to be that same element type ties the
two together. Every contiguous standard container satisfies it, so std::string,
std::vector<char>, std::array<char, N> and std::string_view keep the fast path;
anything else falls back to the iterator-based adapter, which is always correct.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MXDi7NTMKAmoArUZSKMc4T
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

2026-08-28 14:59:30 +00:00

..

nlohmann

Require a container's value_type to match what data() points at

2026-08-28 14:59:30 +00:00