Updates the platform interface for improved extendability.

- Releases new interface making the Geocoding plugin easier to extend and
  implement on different platforms.
- Moves the old interface into the `legacy` folder. This interface will
  remain available but will no longer be maintained. To import the old
  interface use `import 'package:geocoding_platform_interface/legacy/geocoding_platform_interface.dart`.

Author: mvanbeusekom

geocoding_platform_interface/CHANGELOG.md

@@ -1,3 +1,12 @@
+## 4.0.0
+
+- **BREAKING CHANGES:**
+  - Releases new interface making the Geocoding plugin easier to extend and
+    implement on different platforms.
+  - Moves the old interface into the `legacy` folder. This interface will
+    remain available but will no longer be maintained. To import the old
+    interface use `import 'package:geocoding_platform_interface/legacy/geocoding_platform_interface.dart`.
+
 ## 3.2.1
 
 - Fixed analysis warnings from `flutter analyse`.

geocoding_platform_interface/lib/geocoding_platform_interface.dart

@@ -1,3 +1,3 @@
-export 'src/errors/errors.dart';
-export 'src/geocoding_platform_interface.dart';
-export 'src/models/models.dart';
+export 'src/geocoding.dart';
+export 'src/geocoding_platform_factory.dart';
+export 'src/types/types.dart';

geocoding_platform_interface/lib/legacy/geocoding_platform_interface.dart

@@ -0,0 +1,3 @@
+export 'src/errors/errors.dart';
+export 'src/geocoding_platform_interface.dart';
+export 'src/models/models.dart';

geocoding_platform_interface/lib/src/errors/errors.dart renamed to geocoding_platform_interface/lib/legacy/src/errors/errors.dart

@@ -0,0 +1,97 @@
+import 'package:flutter/widgets.dart';
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+
+import 'geocoding_platform_factory.dart';
+import 'types/types.dart';
+
+/// Interface for a platform implementation of a [Geocoding] instance.
+///
+/// Platform implementations should extend this class rather than implement it
+/// as `geocoding` package does not consider newly added methods to be breaking
+/// changes. Extending this class (using `extends`) ensures that the subclass
+/// will get the default implementation, while platform implementations that
+/// `implements` this interface will be broken by newly added
+/// [Geocoding] methods.
+abstract class Geocoding extends PlatformInterface {
+  /// Creates a new [PlatformWebViewController]
+  factory Geocoding(GeocodingCreationParams params) {
+    assert(
+      GeocodingPlatformFactory.instance != null,
+      'A platform implementation for `geocoding` has not been set. Please '
+      'ensure that an implementation of `GeocodingPlatformFactory` has been '
+      'set te `GeocodingPlatformFactory.instance` before use. For unit '
+      'testing, `GeocodingPlatformFactory.instance` can be set with your own '
+      'test implementation.',
+    );
+    final Geocoding geocoding =
+        GeocodingPlatformFactory.instance!.createGeocoding(params);
+    PlatformInterface.verify(geocoding, _token);
+    return geocoding;
+  }
+
+  /// Used by the platform implementation to create a new [Geocoding].
+  ///
+  /// Should only be used by platform implementations because they can't extend
+  /// a class that only contains a factory constructor.
+  @protected
+  Geocoding.implementation(this.params) : super(token: _token);
+
+  static final Object _token = Object();
+
+  /// The parameters used to initialize the [Geocoding] instance.
+  final GeocodingCreationParams params;
+
+  /// Returns a list of [Location] instances found for the supplied address.
+  ///
+  /// In most situations the returned list should only contain one entry.
+  /// However in some situations where the supplied address could not be
+  /// resolved into a single [Location], multiple [Location] instances may be
+  /// returned.
+  Future<List<Location>> locationFromAddress(
+    String address, {
+    Locale? locale,
+  }) {
+    throw UnimplementedError(
+        'locationFromAddress() has not been implementated.');
+  }
+
+  /// Returns true if there is a geocoder implementation present that may return results.
+  /// If true, there is still no guarantee that any individual geocoding attempt will succeed.
+  ///
+  ///
+  /// This method is only implemented on Android, calling this on iOS always
+  /// returns [true].
+  Future<bool> isPresent() {
+    throw UnimplementedError('isPresent() has not been implementated.');
+  }
+
+  /// Returns a list of [Placemark] instances found for the supplied
+  /// coordinates.
+  ///
+  /// In most situations the returned list should only contain one entry.
+  /// However in some situations where the supplied coordinates could not be
+  /// resolved into a single [Placemark], multiple [Placemark] instances may be
+  /// returned.
+  Future<List<Placemark>> placemarkFromCoordinates(
+    double latitude,
+    double longitude, {
+    Locale? locale,
+  }) {
+    throw UnimplementedError(
+        'placemarkFromCoordinates() has not been implementated.');
+  }
+
+  /// Returns a list of [Placemark] instances found for the supplied address.
+  ///
+  /// In most situations the returned list should only contain one entry.
+  /// However in some situations where the supplied address could not be
+  /// resolved into a single [Placemark], multiple [Placemark] instances may be
+  /// returned.
+  Future<List<Placemark>> placemarkFromAddress(
+    String address, {
+    Locale? locale,
+  }) {
+    throw UnimplementedError(
+        'placemarkFromAddress() has not been implementated.');
+  }
+}