# <small>nlohmann::basic_json::</small>swap

```cpp
// (1)
void swap(reference other) noexcept (
    std::is_nothrow_move_constructible<value_t>::value &&
    std::is_nothrow_move_assignable<value_t>::value &&
    std::is_nothrow_move_constructible<json_value>::value &&
    std::is_nothrow_move_assignable<json_value>::value &&
    std::is_nothrow_move_constructible<json_base_class_t>::value &&
    std::is_nothrow_move_assignable<json_base_class_t>::value
);

// (2)
friend void swap(reference left, reference right) noexcept (
    std::is_nothrow_move_constructible<value_t>::value &&
    std::is_nothrow_move_assignable<value_t>::value &&
    std::is_nothrow_move_constructible<json_value>::value &&
    std::is_nothrow_move_assignable<json_value>::value &&
    std::is_nothrow_move_constructible<json_base_class_t>::value &&
    std::is_nothrow_move_assignable<json_base_class_t>::value
);

// (3)
void swap(array_t& other);

// (4)
void swap(object_t& other);

// (5)
void swap(string_t& other);

// (6)
void swap(binary_t& other);

// (7)
void swap(typename binary_t::container_type& other);
```

1. Exchanges the contents of the JSON value with those of `other`. Does not invoke any move, copy, or swap operations on
   individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated. If macro
   [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) is defined to `#!cpp 1`, the
   [`start_pos()`](start_pos.md)/[`end_pos()`](end_pos.md) diagnostic positions are exchanged along with the value.
   The [`json_base_class_t`](json_base_class_t.md) subobject is exchanged along with the value as well, the same way it
   is copied or moved by the copy/move constructors and assignment operators.
2. Exchanges the contents of the JSON value from `left` with those of `right`. Does not invoke any move, copy, or swap
   operations on individual elements. All iterators and references remain valid. The past-the-end iterator is
   invalidated. Implemented as a friend function callable via ADL. If macro
   [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) is defined to `#!cpp 1`, the
   [`start_pos()`](start_pos.md)/[`end_pos()`](end_pos.md) diagnostic positions are exchanged along with the value.
   The [`json_base_class_t`](json_base_class_t.md) subobject is exchanged along with the value as well, the same way it
   is copied or moved by the copy/move constructors and assignment operators.
3. Exchanges the contents of a JSON array with those of `other`. Does not invoke any move, copy, or swap operations on
   individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated. 
4. Exchanges the contents of a JSON object with those of `other`. Does not invoke any move, copy, or swap operations on
   individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
5. Exchanges the contents of a JSON string with those of `other`. Does not invoke any move, copy, or swap operations on
   individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
6. Exchanges the contents of a binary value with those of `other`. Does not invoke any move, copy, or swap operations on
   individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
7. Exchanges the contents of a binary value with those of `other`. Does not invoke any move, copy, or swap operations on
   individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated. Unlike
   version (6), no binary subtype is involved.

## Parameters

`other` (in, out)
:   value to exchange the contents with

`left` (in, out)
:   value to exchange the contents with

`right` (in, out)
:   value to exchange the contents with

## Exception safety

1. No-throw guarantee: this function never throws exceptions.
2. No-throw guarantee: this function never throws exceptions.
3. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
4. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
5. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
6. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
7. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

## Exceptions

1. No-throw guarantee: this function never throws exceptions.
2. No-throw guarantee: this function never throws exceptions.
3. Throws [`type_error.310`](../../home/exceptions.md#jsonexceptiontype_error310) if called on JSON values other than
   arrays; example: `"cannot use swap(array_t&) with boolean"`
4. Throws [`type_error.310`](../../home/exceptions.md#jsonexceptiontype_error310) if called on JSON values other than
   objects; example: `"cannot use swap(object_t&) with boolean"`
5. Throws [`type_error.310`](../../home/exceptions.md#jsonexceptiontype_error310) if called on JSON values other than
   strings; example: `"cannot use swap(string_t&) with boolean"`
6. Throws [`type_error.310`](../../home/exceptions.md#jsonexceptiontype_error310) if called on JSON values other than
   binaries; example: `"cannot use swap(binary_t&) with boolean"`
7. Throws [`type_error.310`](../../home/exceptions.md#jsonexceptiontype_error310) if called on JSON values other than
   binaries; example: `"cannot use swap(binary_t::container_type&) with boolean"`

## Complexity

Constant.

## Examples

??? example "Example: (1, 2) swap JSON values"

    The example below shows how JSON values can be swapped with `swap()`.
    
    ```cpp
    #include <iostream>
    #include <nlohmann/json.hpp>
    
    using json = nlohmann::json;
    
    int main()
    {
        // create two JSON values
        json j1 = {1, 2, 3, 4, 5};
        json j2 = {{"pi", 3.141592653589793}, {"e", 2.718281828459045}};
    
        // swap the values
        j1.swap(j2);
    
        // output the values
        std::cout << "j1 = " << j1 << '\n';
        std::cout << "j2 = " << j2 << '\n';
    }
    
    ```
    
    Output:
    
    ```json
    j1 = {"e":2.718281828459045,"pi":3.141592653589793}
    j2 = [1,2,3,4,5]
    
    ```

??? example "Example: (3) swap array"

    The example below shows how arrays can be swapped with `swap()`.
    
    ```cpp
    #include <iostream>
    #include <nlohmann/json.hpp>
    
    using json = nlohmann::json;
    
    int main()
    {
        // create a JSON value
        json value = {{"array", {1, 2, 3, 4}}};
    
        // create an array_t
        json::array_t array = {"Snap", "Crackle", "Pop"};
    
        // swap the array stored in the JSON value
        value["array"].swap(array);
    
        // output the values
        std::cout << "value = " << value << '\n';
        std::cout << "array = " << array << '\n';
    }
    
    ```
    
    Output:
    
    ```json
    value = {"array":["Snap","Crackle","Pop"]}
    array = [1,2,3,4]
    
    ```

??? example "Example: (4) swap object"

    The example below shows how objects can be swapped with `swap()`.
    
    ```cpp
    #include <iostream>
    #include <nlohmann/json.hpp>
    
    using json = nlohmann::json;
    
    int main()
    {
        // create a JSON value
        json value = { {"translation", {{"one", "eins"}, {"two", "zwei"}}} };
    
        // create an object_t
        json::object_t object = {{"cow", "Kuh"}, {"dog", "Hund"}};
    
        // swap the object stored in the JSON value
        value["translation"].swap(object);
    
        // output the values
        std::cout << "value = " << value << '\n';
        std::cout << "object = " << object << '\n';
    }
    
    ```
    
    Output:
    
    ```json
    value = {"translation":{"cow":"Kuh","dog":"Hund"}}
    object = {"one":"eins","two":"zwei"}
    
    ```

??? example "Example: (5) swap string"

    The example below shows how strings can be swapped with `swap()`.
    
    ```cpp
    #include <iostream>
    #include <nlohmann/json.hpp>
    
    using json = nlohmann::json;
    
    int main()
    {
        // create a JSON value
        json value = { "the good", "the bad", "the ugly" };
    
        // create string_t
        json::string_t string = "the fast";
    
        // swap the object stored in the JSON value
        value[1].swap(string);
    
        // output the values
        std::cout << "value = " << value << '\n';
        std::cout << "string = " << string << '\n';
    }
    
    ```
    
    Output:
    
    ```json
    value = ["the good","the fast","the ugly"]
    string = the bad
    
    ```

??? example "Example: (6) swap binary"

    The example below shows how binary values can be swapped with `swap()`.
    
    ```cpp
    #include <iostream>
    #include <nlohmann/json.hpp>
    
    using json = nlohmann::json;
    
    int main()
    {
        // create a binary value
        json value = json::binary({1, 2, 3});
    
        // create a binary_t
        json::binary_t binary = {{4, 5, 6}};
    
        // swap the object stored in the JSON value
        value.swap(binary);
    
        // output the values
        std::cout << "value = " << value << '\n';
        std::cout << "binary = " << json(binary) << '\n';
    }
    
    ```
    
    Output:
    
    ```json
    value = {"bytes":[4,5,6],"subtype":null}
    binary = {"bytes":[1,2,3],"subtype":null}
    
    ```

## See also

- [std::swap<basic_json\>](std_swap.md)
- [operator=](operator=.md) copy assignment
- [basic_json](basic_json.md) create a JSON value

## Version history

1. Since version 1.0.0. Exchanges the `json_base_class_t` subobject along with the value since version 3.13.0.
2. Since version 1.0.0. Exchanges the `json_base_class_t` subobject along with the value since version 3.13.0.
3. Since version 1.0.0.
4. Since version 1.0.0.
5. Since version 1.0.0.
6. Since version 3.8.0.
7. Since version 3.8.0.