mirror of
https://github.com/nlohmann/json.git
synced 2026-10-08 23:47:13 +00:00
Niels Lohmann
c6ee5a64be
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>
39 lines
1.5 KiB
C++
39 lines
1.5 KiB
C++
#include <iostream>
|
|
#include <nlohmann/json_view.hpp>
|
|
|
|
using json = nlohmann::json;
|
|
using json_editable_document = nlohmann::json_editable_document;
|
|
using json_editable_view = nlohmann::json_editable_view;
|
|
|
|
int main()
|
|
{
|
|
// a deployment plan -- "budget" is written with a trailing zero that has
|
|
// no effect on its value
|
|
const std::string text = R"({
|
|
"release": "2026.09",
|
|
"steps": ["build", "test", "deploy"],
|
|
"budget": 19.90
|
|
})";
|
|
|
|
json_editable_document doc = json_editable_document::parse(text);
|
|
|
|
const std::size_t deploy_index = 2;
|
|
const auto deploy = doc.root()["steps"][deploy_index]; // held across the insert
|
|
|
|
doc.insert(doc.root()["steps"], deploy_index, "smoke-test"); // insert before "deploy"
|
|
|
|
// the held view still refers to "deploy", even though its index moved
|
|
// from 2 to 3, and nothing else in the document was touched
|
|
std::cout << deploy.dump() << '\n';
|
|
std::cout << doc.root().dump(2, ' ', false, json_editable_view::number_format::source) << "\n\n";
|
|
|
|
// the same edit on a plain json value: an index held from before the
|
|
// insert now refers to whatever moved into that slot, and dump()
|
|
// rewrites "budget" to its shortest form even though it was never
|
|
// touched
|
|
json plain = json::parse(text);
|
|
plain["steps"].insert(plain["steps"].begin() + static_cast<std::ptrdiff_t>(deploy_index), "smoke-test");
|
|
std::cout << plain["steps"][deploy_index].dump() << '\n';
|
|
std::cout << plain.dump(2) << '\n';
|
|
}
|