adapt abstract method

A Jetleaf-specific adapter that lifts generic conversion results into strongly-typed values.

Jetleaf's conversion service always returns results as Object (e.g., Map<Object, Object> instead of Map<int, String>). This design avoids runtime type conflicts but requires a way to adapt those values into the precise type expected by the user.

The TypeAdapter abstraction provides that bridge.
It allows both Jetleaf internals and user code to declare how a raw Object from the conversion service should be transformed into a fully typed value.

Why?

• Jetleaf avoids committing to a Dart type at the conversion layer.
• Dart’s type system is strict, so generic Object results need adaptation to their concrete forms.
• Adapters guarantee that values are raised into the expected type at the call site.

Example: Adapting to a typed map

class StringIntMapAdapter extends TypeAdapter<Map<String, int>> {
  @override
  Map<String, int> adapt(Object? source) {
    if (source is Map<Object, Object>) {
      return source.map((k, v) => MapEntry(k as String, v as int));
    }
    throw ArgumentError('Cannot adapt $source to Map<String, int>');
  }
}

final raw = <Object, Object>{'a': 1, 'b': 2};
final adapter = StringIntMapAdapter();
final typed = adapter.adapt(raw); // -> Map<String, int>

Example: Adapting to a domain type

class User {
  final String name;
  final int age;
  User(this.name, this.age);
}

class UserAdapter extends TypeAdapter<User> {
  @override
  User adapt(Object? source) {
    if (source is Map<Object, Object>) {
      return User(source['name'] as String, source['age'] as int);
    }
    throw ArgumentError('Cannot adapt $source to User');
  }
}

Jetleaf itself uses adapters internally to ensure that results from its conversion service are raised to the exact type requested by the user.