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# `rfl::Object`
`rfl::Object<...>` behaves similarly to `std::map<std::string, ...>` and `std::unordered_map<std::string, ...>`.
It will be represented in JSON or other formats as an object:
```cpp
auto bart = rfl::Object<std::string>();
bart["first_name"] = "Bart";
bart["last_name"] = "Simpson";
bart["town"] = "Springfield";
```
This is results in the following JSON string:
```cpp
{"first_name":"Bart","last_name":"Simpson","town":"Springfield"}
```
It supports almost all of the normal features you would expect from such a container. For instance,
you can iterate through it just like any other map:
```cpp
for (const auto& [k, v]: bart) {
std::cout << k << ": " << v << std::endl;
}
```
However, unlike these containers, the order of fields is preserved. It is also possible to have duplicate keys:
```cpp
auto bart = rfl::Object<std::string>();
bart["first_name"] = "Bart";
bart["last_name"] = "Simpson";
bart["town"] = "Springfield";
// Note that you need the .insert(...) method,
// because operator[] would overwrite the
// existing field.
bart.insert("first_name", "Lisa");
```
This results in the following JSON string:
```cpp
{"first_name":"Bart","last_name":"Simpson","town":"Springfield","first_name":"Lisa"}
```
There are three different ways of inserting fields:
- `operator[...]` creates a new field, if a field of this name doesn't already exist, and then assigns it.
- `.insert(...)` inserts a new field at the end, potentially creating duplicate field names. Much like `std::map`, it supports several types of inputs:
- `.insert(std::pair(key, value))`
- `.insert(key, value)`
- `.insert(begin, end)`, where `begin` and `end` are iterators of a container of key-value-pairs
- `.emplace(...)` is an alias for `.insert` that exists primarily for reasons of compatability with standard containers.
There are three different ways of accessing fields:
- `operator[...]` creates a new field, if a field of this name doesn't already exist.
- `.at(...)` throws an exception, if field of this name doesn't exist.
- `.get(...)` returns an `rfl::Result` wrapping the field, or an `rfl::Error` if the field doesn't exist.
Note that it is most efficient, if you access fields in the order that they were placed.
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