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basic_json_document gets a second template parameter, Editable (false by default), plus the aliases json_editable_document, json_editable_view, ordered_json_editable_document and ordered_json_editable_view. Editable documents can change values and structure without rewriting the source text: set()/push_back() on values, keys, array indices and JSON pointers; insert() before an array element; erase() of an object key, array index or JSON pointer. New values and element sequences go into edit storage that the document owns and never moves, so views keep referring to their value across edits and a parsed node never moves. Read-only documents walk the plain node array and are unaffected. Strings are checked for UTF-8 on entry, so dump() of an editable document never throws type_error.316. Binary values cannot be stored (type_error.319). A seeded differential test applies random edits to an editable document and to the equivalent ordered_json and compares both after every step. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
25 lines
925 B
C++
25 lines
925 B
C++
#include <iostream>
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#include <nlohmann/json_view.hpp>
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using json = nlohmann::json;
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using json_editable_document = nlohmann::json_editable_document;
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int main()
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{
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// "events" starts out null -- the first push_back() turns it into an
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// array, exactly like set() turns a null object member into an object
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json_editable_document doc = json_editable_document::parse(R"({"source": "sensor-1", "events": null})");
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const auto first = doc.push_back(doc.root()["events"], json{{"type", "start"}, {"t", 0}});
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for (int t = 1; t <= 3; ++t)
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{
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doc.push_back(doc.root()["events"], json{{"type", "tick"}, {"t", t}});
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}
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// push_back() never moves an existing element: a view taken from an
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// earlier call still refers to the same element after later ones
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std::cout << first.dump() << '\n';
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std::cout << doc.root()["events"].size() << '\n';
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std::cout << doc.root().dump(2) << '\n';
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}
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