This will make it less painful to add additional properties, which
should persist across writes, such as `name`.
Conflicts:
activerecord/lib/active_record/attribute_set.rb
Moved `Builder` to its own file, as it started looking very weird once I
added private methods to the `AttributeSet` class and the `Builder`
class started to grow.
Would like to refactor `fetch_value` to change to
```ruby
self[name].value(&block)
```
But that requires the attributes to know about their name, which they
currently do not.
Adding `# :nodoc:` to the parent `class` / `module` is not going
to ignore nested classes or modules.
There is a modifier `# :nodoc: all` but sadly the containing class
or module will continue to be in the docs.
/cc @sgrif
There's a lot more that can be moved to these, but this felt like a good
place to introduce the object. Plans are:
- Remove all knowledge of type casting from the columns, beyond a
reference to the cast_type
- Move type_cast_for_database to these objects
- Potentially make them mutable, introduce a state machine, and have
dirty checking handled here as well
- Move `attribute`, `decorate_attribute`, and anything else that
modifies types to mess with this object, not the columns hash
- Introduce a collection object to manage these, reduce allocations, and
not require serializing the types
