
## rtti

### Synopsis

Defined in <boost/openmethod/policies/basic_policy.hpp>.

```c++
namespace boost::openmethod::policies {

struct rtti : policy {};

} // boost::openmethod::policies
```

### Description

The `rtti` policy provides type information for classes and objects, implements
downcast in presence of virtual inheritance, and writes descriptions of types to
an `ostream`-like object.

### Requirements

#### is_polymorphic

```c++
template<class Class> static constexpr bool is_polymorphic;
```

`true` if `Class` is polymorphic.

#### static_type

```c++
template<class Class> static auto static_type() -> type_id;
```

Returns a `type_id` for `Class`.

#### dynamic_type

```c++
template<class Class> static auto dynamic_type(const Class& obj) -> type_id;
```

Returns a `type_id` for an object's dynamic type.

#### type_name

```c++
template<typename Stream>
static auto type_name(type_id type, Stream& stream) -> void;
```

Writes a description of `type` to `stream`.

This requirement is optional. `rtti` provides a default implementation that writes `typeid({type})` to `stream`.

#### type_index

```c++
static auto type_index(type_id type) -> /* unspecified */;
```

Returns a unique key for `type`. Required only for RTTI systems that assign more
than one type "identifiers" to a type. For example, standard RTTI allows
implementations to have multiple instances of `std::type_info` for the same
type.

#### dynamic_cast_ref

```c++
template<typename D, typename B>
static auto dynamic_cast_ref(B&& obj) -> D;
```

Casts `obj` to `D`. Required only if using virtual inheritance.
