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57 lines
1.5 KiB
Markdown
57 lines
1.5 KiB
Markdown
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# basic_json::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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## 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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## 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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## Version history
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- Since version 2.0.8.
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