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>
75 lines
2.4 KiB
Markdown
75 lines
2.4 KiB
Markdown
# <small>nlohmann::basic_json::</small>emplace
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```cpp
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template<class... Args>
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std::pair<iterator, bool> emplace(Args&& ... args);
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```
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Inserts a new element into a JSON object constructed in-place with the given `args` if there is no element with the key
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in the container. If the function is called on a JSON null value, an empty object is created before appending the value
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created from `args`.
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## Template parameters
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`Args`
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: compatible types to create a `basic_json` object
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## Iterator invalidation
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For [`ordered_json`](../ordered_json.md), adding a value to an object can yield a reallocation, in which case all
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iterators (including the `end()` iterator) and all references to the elements are invalidated.
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## Parameters
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`args` (in)
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: arguments to forward to a constructor of `basic_json`
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## Return value
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a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and
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a `#!cpp bool` denoting whether the insertion took place.
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## Exception safety
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Strong guarantee: if an exception is thrown, there are no changes to any JSON value. As an exception, a `#!json null`
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value is converted to an empty object before the element is added and keeps that type if adding the element throws.
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## Exceptions
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Throws [`type_error.311`](../../home/exceptions.md#jsonexceptiontype_error311) when called on a type other than JSON
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object or `#!json null`; example: `"cannot use emplace() with number"`
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## Complexity
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Logarithmic in the size of the container, O(log(`size()`)).
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## Examples
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??? example
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The example shows how `emplace()` can be used to add elements to a JSON object. Note how the `#!json null` value was
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silently converted to a JSON object. Further note how no value is added if there was already one value stored with
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the same key.
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```cpp
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--8<-- "examples/emplace.cpp"
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```
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Output:
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```json
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--8<-- "examples/emplace.output"
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```
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## See also
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- [`emplace_back`](emplace_back.md) - add a value to an array
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- [`insert`](insert.md) - add values to an array/object
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- [Modifying values](../../features/modifying_values.md) - the article on modifying values
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## Version history
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- Added in version 2.0.8.
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- Fixed in version 3.13.0: for [`ordered_json`](../ordered_json.md), the value could previously only be passed as an
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rvalue; it can now also be passed as an lvalue or a `#!cpp const` lvalue, matching the behavior of `json`.
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