5352856f04
* Add key_compare member to ordered_map
* Replace == with key_compare in ordered_map
* Expose the actual comparison function used by object_t
nlohmann::ordered_map uses a different comparison function than the one
provided via template parameter.
* Introduce a type trait to detect if object_t has a key_compare member.
* Rename object_comparator_t to default_object_comparator_t.
* Add object_comparator_t to be conditionally defined as
object_t::key_compare, if available, or default_object_comparator_t
otherwise.
* Update the documentation accordingly.
Co-authored-by: Niels Lohmann <niels.lohmann@gmail.com>
* Add type traits to check if a type is usable as object key
Add type trait to check:
* if a type is a specialization of a template.
* if a type is a json_pointer.
* if a type is a basic_json::{const_,}iterator.
* if two types are comparable using a given comparison functor.
* if a type is comparable to basic_json::object_t::key_type.
* if a type has a member type is_transparent.
* if a type is usable as object key.
* if a type has an erase() function accepting a given KeyType.
Co-authored-by: Niels Lohmann <niels.lohmann@gmail.com>
* Rework basic_json element access to accept more key types
Rework basic_json element access member functions and operators to
accept any type that meets the requirements defined by type trait
detail::is_usable_as_key_type.
Member functions and operators:
* at()
* operator[]
* value()
* erase()
* find()
* count()
* contains()
Update documentation to reflect these changes.
Add unit tests to excercise the new functions using std::string_view.
Co-authored-by: Niels Lohmann <niels.lohmann@gmail.com>
Co-authored-by: Niels Lohmann <niels.lohmann@gmail.com>
105 lines
2.9 KiB
Markdown
105 lines
2.9 KiB
Markdown
# <small>nlohmann::basic_json::</small>contains
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```cpp
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// (1)
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bool contains(const typename object_t::key_type& key) const;
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// (2)
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template<typename KeyType>
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bool contains(KeyType&& key) const;
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// (3)
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bool contains(const json_pointer& ptr) const;
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```
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1. Check whether an element exists in a JSON object with a key equivalent to `key`. If the element is not found or the
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JSON value is not an object, `#!cpp false` is returned.
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2. See 1. This overload is only available if `KeyType` is comparable with `#!cpp typename object_t::key_type` and
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`#!cpp typename object_comparator_t::is_transparent` denotes a type.
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3. Check whether the given JSON pointer `ptr` can be resolved in the current JSON value.
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## Template parameters
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`KeyType`
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: A type for an object key other than [`json_pointer`](../json_pointer/index.md) that is comparable with
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[`string_t`](string_t.md) using [`object_comparator_t`](object_comparator_t.md).
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This can also be a string view (C++17).
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## Parameters
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`key` (in)
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: key value to check its existence.
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`ptr` (in)
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: JSON pointer to check its existence.
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## Return value
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1. `#!cpp true` if an element with specified `key` exists. If no such element with such key is found or the JSON value
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is not an object, `#!cpp false` is returned.
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2. See 1.
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3. `#!cpp true` if the JSON pointer can be resolved to a stored value, `#!cpp false` otherwise.
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## Exception safety
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Strong exception safety: if an exception occurs, the original value stays intact.
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## Exceptions
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1. The function does not throw exceptions.
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2. The function does not throw exceptions.
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3. The function can throw the following exceptions:
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- Throws [`parse_error.106`](../../home/exceptions.md#jsonexceptionparse_error106) if an array index begins with
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`0`.
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- Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) if an array index was not a
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number.
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## Complexity
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Logarithmic in the size of the JSON object.
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## Notes
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1. This method always returns `#!cpp false` when executed on a JSON type that is not an object.
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2. This method can be executed on any JSON value type.
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!!! info "Postconditions"
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If `#!cpp j.contains(x)` returns `#!c true` for a key or JSON pointer `x`, then it is safe to call `j[x]`.
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## Examples
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??? example "Example (1) check with key"
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The example shows how `contains()` is used.
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```cpp
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--8<-- "examples/contains.cpp"
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```
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Output:
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```json
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--8<-- "examples/contains.output"
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```
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??? example "Example (3) check with JSON pointer"
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The example shows how `contains()` is used.
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```cpp
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--8<-- "examples/contains_json_pointer.cpp"
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```
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Output:
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```json
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--8<-- "examples/contains_json_pointer.output"
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```
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## Version history
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1. Added in version 3.11.0.
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2. Added in version 3.6.0. Extended template `KeyType` to support comparable types in version 3.11.0.
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3. Added in version 3.7.0.
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