## error_handler

### Synopsis

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

```c++

namespace boost::openmethod {

namespace policies {

struct error_handler;

}

struct openmethod_error {};

struct not_implemented_error : openmethod_error {
    type_id method;
    std::size_t arity;
    static constexpr std::size_t max_types = 16;
    type_id types[max_types];
};

struct unknown_class_error : openmethod_error {
    type_id type;
};

struct hash_search_error : openmethod_error {
    std::size_t attempts;
    std::size_t buckets;
};

struct type_mismatch_error : openmethod_error {
    type_id type;
};

}
```

### Description

`error_handler` is a policy that handles errors.

When an error is encountered, either during `initialize` or method dispatch, the
program is terminated via a call to `abort`. If this policy is present in the
policy, its `error` function is called with an error object. It can prevent
termination by throwing an exception.

### Requirements

Implementations of `error_handler` must provide the following functions:

#### error

```c++
static auto error(const T&) -> void;
```