nlohmann::basic_json_document::basic_json_document¶

// (1)
basic_json_document() = default;

// (2)
basic_json_document(basic_json_document&& other) noexcept = default;

// (3)
basic_json_document(const basic_json_document&) = delete;

1. Creates an empty (discarded) document: root() returns a discarded view, and is_discarded() is true.
2. Move constructor. Takes over other's index and, if owned, its text; other is left as an empty document. Views taken from other before the move remain valid, because the index is heap-allocated independently of the basic_json_document object.
3. basic_json_document is move-only. Copying is disabled because of its cost: a copy would duplicate the whole index, the decoded-string buffer, and the owned text, while a move is enough in every use we know of.

Parameters¶

other (in)

another document to move the index and text from

Exception safety¶

No-throw guarantee: the default and move constructors never throw exceptions.

Complexity¶

Constant.

Examples¶

#include <iostream>
#include <utility>
#include <nlohmann/json_view.hpp>

using json_document = nlohmann::json_document;

int main()
{
    std::cout << std::boolalpha;

    // the default constructor creates an empty (discarded) document
    json_document empty;
    std::cout << empty.is_discarded() << '\n';

    // json_document is move-only: parse() itself returns by value (moved out),
    // and a document can be moved again, e.g. into a container
    json_document doc = json_document::parse(R"({"a": 1})");
    json_document moved = std::move(doc);
    std::cout << moved.root().is_object() << '\n';

    // copying is disabled at compile time:
    // json_document another = moved; // does not compile
}

true
true

See also¶

• parse - deserialize from a compatible input
• is_discarded - return whether the last parse failed

Version history¶

• Added in version 3.13.0 unreleased.