Niels Lohmann
a47170346a
* docs: new design for the documentation site Apply the brand to the Material for MkDocs site: Inter and JetBrains Mono served by the site (upright and real italic), brand colours, blue header band with the syntax pattern, wordmark in the header, new home page (hero, cards, animated feature tour), 404 page, polish for tabs, search, footer, focus rings, tables and code blocks, and theme features (code copy, previous/next footer, TOC follow, search suggestions). Draw the number railroad diagram, the parser callback events and the iterator illustrations as inline SVGs that follow the light and dark scheme. The generator scripts are in docs/mkdocs/scripts/figures; the feature slideshow (json-light.svg, json-dark.svg, replacing json.gif on the home page) is built by docs/mkdocs/scripts/slideshow. Decision nodes in five flowcharts become hexagons, which need far less room. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: add figures, table captions and a macro chooser - Figures with numbered captions: SAX stepper, json_view layout and edit stepper, exception map, JSON pointer and patch walkers, QA pipeline, scaling and binary size charts, roadmap lanes, release timeline, integration decision tree and namespace builder - Table captions (nj-table-caption) on 9 pages - Compile times: modules and PCH charts, filesystem section, re-measured Figure 1, links between features/modules.md and compile_times.md - Interactive macro chooser for features/arbitrary_types.md - Link check: exclude URLs that answer the plugin with 400/401/419 or are dead (customers.md) Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: macro chooser generates adl_serializer for non-default-constructible types Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: cross-link concept pages and API pages in See also sections Add See also links in both directions between the concept pages (features, home, integration) and the API pages, write API links in code font, give every entry a comment after a dash, and show the callback event figure on the parser callbacks page. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: address review comments on the new design - Home: add a "Latest release" button - Sponsors: update the list and group it by tier - Features: list all feature pages on the index page - Releases: add highlights per release, link the 4.0 roadmap, add the first commit to the timeline - Exceptions: prefix all example messages with the exception name - API: no code font for format names in the See also links of the to_/from_ pages - Merge Patch: show the document before, the patch, and the result - Replace "--" with typographic dashes, mark external links with an icon, center Mermaid diagrams Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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2.9 KiB
nlohmann::basic_json_view::get_to
template<typename T>
T& get_to(T& v) const;
Converts the value to T and stores it in v, in one of three ways:
- For the types that
get<T>()converts directly — arithmetic types,#!cpp bool,#!cpp std::nullptr_t,string_view_t,#!cpp std::basic_string,BasicJsonType,basic_json_view, vectors of these, and maps of views —vis assigned:#!cpp v = get<T>(). - For a type whose
from_json()accepts views (seeget<T>()), thatfrom_json()is called with the view and the existingv, without building aBasicJsonTypevalue. - For every other type, the subtree is built into a
BasicJsonTypevalue and#!cpp materialize().get_to(v)is called, i.e.from_json()is invoked with the existingv, exactly asBasicJsonType::get_to()does.
Template parameters
T- the type to convert the value to
Parameters
v(out)- the variable to store the converted value in
Return value
v, allowing calls to chain
Exception safety
- For the directly converted types: strong exception safety. If an exception is thrown,
vis not modified. - For every other type: as for
BasicJsonType::get_to().materialize()throws beforevis touched, but afrom_json()that throws may leavevpartly modified.
Exceptions
- For the directly converted types: whatever
get<T>()throws for the same value andT. - For every other type: whatever
materialize()andBasicJsonType::get_to()throw.
Complexity
- For the directly converted types: whatever
get<T>()has for the sameT. - For every other type: that of
materialize(), plus that ofBasicJsonType::get_to().
Notes
The difference between the two ways matters for a from_json() that sets only the fields present in the JSON: since
it runs on the existing v, the other fields of v keep their values, whereas assigning get<T>() would replace
them with those of a default-constructed T.
Examples
??? example
The example below reads several fields of a service configuration directly into existing variables, then uses
the returned reference to fold the `#!cpp host`/`#!cpp port` pair into a single string in the same expression.
```cpp
--8<-- "examples/basic_json_view__get_to.cpp"
```
Output:
```json
--8<-- "examples/basic_json_view__get_to.output"
```
See also
get- convert the value to a given typeBasicJsonType::get_to- the corresponding function ofbasic_json- Zero-copy JSON views - which conversions avoid building a basic_json value
Version history
- Added in version 3.13.0.