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Implement support for string_view (attempt no. 3) (#3423)

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* 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>
This commit is contained in:
Florian Albrechtskirchinger
2022-04-29 21:40:02 +02:00
committed by GitHub
parent ee51661481
commit 5352856f04
26 changed files with 1517 additions and 305 deletions
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31
doc/mkdocs/docs/api/basic_json/find.md
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@@ -1,20 +1,28 @@
# <small>nlohmann::basic_json::</small>find
```cpp
template<typename KeyT>
iterator find(KeyT&& key);
// (1)
iterator find(const typename object_t::key_type& key);
const_iterator find(const typename object_t::key_type& key) const;
template<typename KeyT>
const_iterator find(KeyT&& key) const;
// (2)
template<typename KeyType>
iterator find(KeyType&& key);
template<typename KeyType>
const_iterator find(KeyType&& key) const;
```
Finds an element in a JSON object with key equivalent to `key`. If the element is not found or the JSON value is not an
object, `end()` is returned.
1. Finds an element in a JSON object with a key equivalent to `key`. If the element is not found or the
JSON value is not an object, `end()` is returned.
2. See 1. This overload is only available if `KeyType` is comparable with `#!cpp typename object_t::key_type` and
`#!cpp typename object_comparator_t::is_transparent` denotes a type.
## Template parameters
`KeyT`
: A type for an object key.
`KeyType`
: A type for an object key other than [`json_pointer`](../json_pointer/index.md) that is comparable with
[`string_t`](string_t.md) using [`object_comparator_t`](object_comparator_t.md).
This can also be a string view (C++17).
## Parameters
@@ -23,8 +31,8 @@ object, `end()` is returned.
## Return value
Iterator to an element with key equivalent to `key`. If no such element is found or the JSON value is not an object,
past-the-end (see `end()`) iterator is returned.
Iterator to an element with a key equivalent to `key`. If no such element is found or the JSON value is not an object,
a past-the-end iterator (see `end()`) is returned.
## Exception safety
@@ -60,4 +68,5 @@ This method always returns `end()` when executed on a JSON type that is not an o
## Version history
- Added in version 1.0.0.
1. Added in version 3.11.0.
2. Added in version 1.0.0. Changed to support comparable types in version 3.11.0.