📝 add more missing examples
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docs/examples/from_json__default_constructible.cpp
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docs/examples/from_json__default_constructible.cpp
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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namespace ns
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{
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// a simple struct to model a person
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struct person
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{
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std::string name;
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std::string address;
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int age;
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};
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} // namespace ns
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namespace ns
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{
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void from_json(const json& j, person& p)
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{
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j.at("name").get_to(p.name);
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j.at("address").get_to(p.address);
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j.at("age").get_to(p.age);
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}
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} // namespace ns
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int main()
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{
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json j;
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j["name"] = "Ned Flanders";
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j["address"] = "744 Evergreen Terrace";
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j["age"] = 60;
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auto p = j.get<ns::person>();
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std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl;
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}
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1
docs/examples/from_json__default_constructible.output
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docs/examples/from_json__default_constructible.output
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Ned Flanders (60) lives in 744 Evergreen Terrace
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53
docs/examples/from_json__non_default_constructible.cpp
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docs/examples/from_json__non_default_constructible.cpp
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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namespace ns
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{
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// a simple struct to model a person (not default constructible)
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struct person
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{
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person(std::string n, std::string a, int aa)
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: name(std::move(n)), address(std::move(a)), age(aa)
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{}
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std::string name;
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std::string address;
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int age;
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};
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} // namespace ns
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namespace nlohmann
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{
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template <>
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struct adl_serializer<ns::person>
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{
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static ns::person from_json(const json& j)
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{
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return {j.at("name"), j.at("address"), j.at("age")};
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}
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// Here's the catch! You must provide a to_json method! Otherwise, you
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// will not be able to convert person to json, since you fully
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// specialized adl_serializer on that type
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static void to_json(json& j, ns::person p)
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{
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j["name"] = p.name;
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j["address"] = p.address;
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j["age"] = p.age;
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}
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};
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} // namespace nlohmann
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int main()
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{
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json j;
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j["name"] = "Ned Flanders";
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j["address"] = "744 Evergreen Terrace";
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j["age"] = 60;
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auto p = j.get<ns::person>();
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std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl;
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}
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@ -0,0 +1 @@
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Ned Flanders (60) lives in 744 Evergreen Terrace
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32
docs/examples/to_json.cpp
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docs/examples/to_json.cpp
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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namespace ns
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{
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// a simple struct to model a person
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struct person
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{
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std::string name;
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std::string address;
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int age;
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};
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} // namespace ns
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namespace ns
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{
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void to_json(json& j, const person& p)
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{
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j = json{ {"name", p.name}, {"address", p.address}, {"age", p.age} };
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}
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} // namespace ns
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int main()
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{
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ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
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json j = p;
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std::cout << j << std::endl;
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}
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1
docs/examples/to_json.output
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docs/examples/to_json.output
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{"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
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@ -14,8 +14,8 @@ noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), detail::identity_
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-> decltype(::nlohmann::from_json(std::forward<BasicJsonType>(j), detail::identity_tag<TargetType> {}))
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```
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This function is usually called by the [`get()`](../basic_json/get.md) function of the
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[basic_json](../basic_json) class (either explicit or via conversion operators).
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This function is usually called by the [`get()`](../basic_json/get.md) function of the [basic_json](../basic_json)
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class (either explicit or via conversion operators).
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1. This function is chosen for default-constructible value types.
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2. This function is chosen for value types which are not default-constructible.
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@ -32,9 +32,41 @@ This function is usually called by the [`get()`](../basic_json/get.md) function
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Copy of the JSON value, converted to `ValueType`
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!!! note
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## Examples
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This documentation page is a stub.
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??? example "Example: (1) Default-constructible type"
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The example below shows how a `from_json` function can be implemented for a user-defined type. This function is
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called by the `adl_serializer` when `get<ns::person>()` is called.
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```cpp
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--8<-- "examples/from_json__default_constructible.cpp"
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```
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Output:
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```json
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--8<-- "examples/from_json__default_constructible.output"
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```
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??? example "Example: (2) Non-default-constructible type"
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The example below shows how a `from_json` is implemented as part of a specialization of the `adl_serializer` to
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realize the conversion of a non-default-constructible type.
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```cpp
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--8<-- "examples/from_json__non_default_constructible.cpp"
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```
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Output:
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```json
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--8<-- "examples/from_json__non_default_constructible.output"
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```
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## See also
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- [to_json](to_json.md)
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## Version history
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@ -17,9 +17,26 @@ This function is usually called by the constructors of the [basic_json](../basic
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`val` (in)
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: value to read from
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!!! note
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## Examples
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This documentation page is a stub.
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??? example
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The example below shows how a `to_json` function can be implemented for a user-defined type. This function is called
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by the `adl_serializer` when the constructor `basic_json(ns::person)` is called.
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```cpp
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--8<-- "examples/to_json.cpp"
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```
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Output:
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```json
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--8<-- "examples/to_json.output"
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```
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## See also
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- [from_json](from_json.md)
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## Version history
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@ -19,6 +19,23 @@ using json_serializer = JSONSerializer<T, SFINAE>;
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The default values for `json_serializer` is [`adl_serializer`](../adl_serializer).
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## Examples
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??? example
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The example below shows how a conversion of a non-default-constructible type is implemented via a specialization of
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the `adl_serializer`.
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```cpp
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--8<-- "examples/from_json__non_default_constructible.cpp"
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```
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Output:
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```json
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--8<-- "examples/from_json__non_default_constructible.output"
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```
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## Version history
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- Since version 2.0.0.
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@ -10,7 +10,7 @@ namespace ns {
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std::string address;
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int age;
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};
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}
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} // namespace ns
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ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
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