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Niels Lohmann
14afaca083
auto v = json_document::parse(text).root() compiled and left the view dangling. Delete the overload for rvalue documents, take a named document in the tests, and document the lifetime rule. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
1.8 KiB
1.8 KiB
nlohmann::basic_json_document::root
// (1)
view_type root() const& noexcept;
// (2)
view_type root() const&& = delete;
- Returns a view of the root value of the document.
- Deleted: the view of a temporary document would dangle.
Return value
A view_type (i.e. #!cpp basic_json_view<BasicJsonType>) for the root value, or a
discarded view if the document is discarded.
Exception safety
No-throw guarantee: this function never throws exceptions.
Complexity
Constant.
Notes
Lifetime. A view refers into the document, so the document must outlive it. root() can therefore only be called
on a document that has a name (an lvalue); calling it on a temporary does not compile:
auto v = json_document::parse(text).root(); // error: the document is destroyed at the end of the statement
auto doc = json_document::parse(text); // OK: keep the document alive
auto v = doc.root();
root() is a cheap handle into the document's index, not a copy of anything; call it as often as needed. The
returned view is valid under the same conditions as any other view of the document -- see
Object inspection -- in particular, it is invalidated by the next
read() or shrink_to_fit() on this document.
Examples
??? example
```cpp
--8<-- "examples/basic_json_document__root.cpp"
```
Output:
```json
--8<-- "examples/basic_json_document__root.output"
```
See also
- is_discarded - return whether the last parse failed
- materialize - build the
BasicJsonTypevalue of a subtree
Version history
- Added in version 3.13.0.