DRY up implementation of TypeHelper impls that map to String

Author: kevmoo

json_serializable/lib/src/type_helpers/big_int_helper.dart

@@ -3,44 +3,20 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/element/type.dart';
-import 'package:source_gen/source_gen.dart' show TypeChecker;
+
 import '../type_helper.dart';
+import 'to_from_string.dart';
 
 class BigIntHelper extends TypeHelper {
   const BigIntHelper();
 
   @override
   String serialize(
-      DartType targetType, String expression, TypeHelperContext context) {
-    if (!_matchesType(targetType)) {
-      return null;
-    }
-
-    final buffer = StringBuffer(expression);
-
-    if (context.nullable) {
-      buffer.write('?');
-    }
-
-    buffer.write('.toString()');
-
-    return buffer.toString();
-  }
+          DartType targetType, String expression, TypeHelperContext context) =>
+      bigIntString.serialize(targetType, expression, context.nullable);
 
   @override
   String deserialize(
-      DartType targetType, String expression, TypeHelperContext context) {
-    if (!_matchesType(targetType)) {
-      return null;
-    }
-
-    return commonNullPrefix(
-      context.nullable,
-      expression,
-      'BigInt.parse($expression as String)',
-    ).toString();
-  }
+          DartType targetType, String expression, TypeHelperContext context) =>
+      bigIntString.deserialize(targetType, expression, context.nullable, false);
 }
-
-bool _matchesType(DartType type) =>
-    const TypeChecker.fromUrl('dart:core#BigInt').isExactlyType(type);

json_serializable/lib/src/type_helpers/date_time_helper.dart

@@ -3,43 +3,21 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/element/type.dart';
-import 'package:source_gen/source_gen.dart' show TypeChecker;
 
 import '../type_helper.dart';
+import 'to_from_string.dart';
 
 class DateTimeHelper extends TypeHelper {
   const DateTimeHelper();
 
   @override
   String serialize(
-      DartType targetType, String expression, TypeHelperContext context) {
-    if (!_matchesType(targetType)) {
-      return null;
-    }
-
-    final buffer = StringBuffer(expression);
-
-    if (context.nullable) {
-      buffer.write('?');
-    }
-
-    buffer.write('.toIso8601String()');
-
-    return buffer.toString();
-  }
+          DartType targetType, String expression, TypeHelperContext context) =>
+      dateTimeString.serialize(targetType, expression, context.nullable);
 
   @override
   String deserialize(
-      DartType targetType, String expression, TypeHelperContext context) {
-    if (!_matchesType(targetType)) {
-      return null;
-    }
-
-    return commonNullPrefix(context.nullable, expression,
-            'DateTime.parse($expression as String)')
-        .toString();
-  }
+          DartType targetType, String expression, TypeHelperContext context) =>
+      dateTimeString.deserialize(
+          targetType, expression, context.nullable, false);
 }
-
-bool _matchesType(DartType type) =>
-    const TypeChecker.fromUrl('dart:core#DateTime').isExactlyType(type);

json_serializable/lib/src/type_helpers/to_from_string.dart

@@ -0,0 +1,72 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analyzer/dart/element/type.dart';
+import 'package:source_gen/source_gen.dart';
+
+import '../type_helper.dart';
+
+const bigIntString = ToFromStringHelper(
+  'BigInt.parse',
+  'toString()',
+  TypeChecker.fromUrl('dart:core#BigInt'),
+);
+
+const dateTimeString = ToFromStringHelper(
+  'DateTime.parse',
+  'toIso8601String()',
+  TypeChecker.fromUrl('dart:core#DateTime'),
+);
+
+const uriString = ToFromStringHelper(
+  'Uri.parse',
+  'toString()',
+  TypeChecker.fromUrl('dart:core#Uri'),
+);
+
+/// Package-internal helper that unifies implementations of [Type]s that convert
+/// trivially to-from [String].
+class ToFromStringHelper {
+  /// The function or constructor to call when creating the associated type.
+  ///
+  /// Assumed to have one parameter of type [String].
+  ///
+  /// Example: `MyClass.parse`
+  final String _parse;
+
+  /// Represents an invocation – property access or function call – on an
+  /// instance of the target type that returns [String].
+  ///
+  /// Examples: `toString()` for a function or `stringValue` for a property.
+  final String _toString;
+  final TypeChecker _checker;
+
+  const ToFromStringHelper(this._parse, this._toString, this._checker);
+
+  bool matches(DartType type) => _checker.isExactlyType(type);
+
+  String serialize(DartType type, String expression, bool nullable) {
+    if (!matches(type)) {
+      return null;
+    }
+
+    if (nullable) {
+      expression = '$expression?';
+    }
+
+    return '$expression.$_toString';
+  }
+
+  String deserialize(
+      DartType type, String expression, bool nullable, bool isString) {
+    if (!matches(type)) {
+      return null;
+    }
+
+    final parseParam = isString ? expression : '$expression as String';
+
+    return commonNullPrefix(nullable, expression, '$_parse($parseParam)')
+        .toString();
+  }
+}

json_serializable/lib/src/type_helpers/uri_helper.dart

@@ -3,43 +3,20 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/element/type.dart';
-import 'package:source_gen/source_gen.dart' show TypeChecker;
 
 import '../type_helper.dart';
+import 'to_from_string.dart';
 
 class UriHelper extends TypeHelper {
   const UriHelper();
 
   @override
   String serialize(
-      DartType targetType, String expression, TypeHelperContext context) {
-    if (!_matchesType(targetType)) {
-      return null;
-    }
-
-    final buffer = StringBuffer(expression);
-
-    if (context.nullable) {
-      buffer.write('?');
-    }
-
-    buffer.write('.toString()');
-
-    return buffer.toString();
-  }
+          DartType targetType, String expression, TypeHelperContext context) =>
+      uriString.serialize(targetType, expression, context.nullable);
 
   @override
   String deserialize(
-      DartType targetType, String expression, TypeHelperContext context) {
-    if (!_matchesType(targetType)) {
-      return null;
-    }
-
-    return commonNullPrefix(
-            context.nullable, expression, 'Uri.parse($expression as String)')
-        .toString();
-  }
+          DartType targetType, String expression, TypeHelperContext context) =>
+      uriString.deserialize(targetType, expression, context.nullable, false);
 }
-
-bool _matchesType(DartType type) =>
-    const TypeChecker.fromUrl('dart:core#Uri').isExactlyType(type);