DRY up common logic for handling nullable

Author: kevmoo

lib/src/type_helpers/date_time_helper.dart

@@ -1,6 +1,7 @@
 import 'package:analyzer/dart/element/type.dart';
 import 'package:source_gen/source_gen.dart' show TypeChecker;
 import '../type_helper.dart';
+import 'type_helper_utils.dart';
 
 class DateTimeHelper extends TypeHelper {
   const DateTimeHelper();
@@ -28,14 +29,8 @@ class DateTimeHelper extends TypeHelper {
       return null;
     }
 
-    var buffer = new StringBuffer();
-
-    if (nullable) {
-      buffer.write("$expression == null ? null : ");
-    }
-
-    buffer.write("DateTime.parse($expression as String)");
-    return buffer.toString();
+    return commonNullPrefix(
+        nullable, expression, "DateTime.parse($expression as String)");
   }
 }
 

lib/src/type_helpers/enum_helper.dart

@@ -1,6 +1,6 @@
 import 'package:analyzer/dart/element/type.dart';
 import '../type_helper.dart';
-import '../utils.dart';
+import 'type_helper_utils.dart';
 
 class EnumHelper extends TypeHelper {
   const EnumHelper();

lib/src/type_helpers/json_helper.dart

@@ -1,6 +1,7 @@
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import '../type_helper.dart';
+import 'type_helper_utils.dart';
 
 class JsonHelper extends TypeHelper {
   const JsonHelper();
@@ -43,11 +44,7 @@ class JsonHelper extends TypeHelper {
     // github.com/dart-lang/json_serializable/issues/19
     var result = "new ${targetType.name}.fromJson($expression$asCast)";
 
-    if (nullable) {
-      result = "$expression == null ? null : " + result;
-    }
-
-    return result;
+    return commonNullPrefix(nullable, expression, result);
   }
 }
 

lib/src/type_helpers/map_helper.dart

@@ -1,6 +1,7 @@
 import 'package:analyzer/dart/element/type.dart';
 import 'package:source_gen/source_gen.dart' show TypeChecker;
 import '../type_helper.dart';
+import 'type_helper_utils.dart';
 
 /// Name used for closure argument when generating calls to `map`.
 final _closureArg = "e";
@@ -41,11 +42,7 @@ class MapHelper extends TypeHelper {
           "$expression.keys,"
           "$expression.values.map(($_closureArg) => $subFieldValue))";
 
-      if (nullable) {
-        result = "$expression == null ? null :" + result;
-      }
-
-      return result;
+      return commonNullPrefix(nullable, expression, result);
     }
     throw new UnsupportedTypeError(targetType, expression);
   }
@@ -85,12 +82,7 @@ class MapHelper extends TypeHelper {
       // No mapping of the values is required!
 
       var result = "new Map<String, $valueArg>.from($expression as Map)";
-
-      if (nullable) {
-        result = "$expression == null ? null :" + result;
-      }
-
-      return result;
+      return commonNullPrefix(nullable, expression, result);
     }
 
     // In this case, we're going to create a new Map with matching reified
@@ -102,11 +94,7 @@ class MapHelper extends TypeHelper {
         "($expression as Map<String, dynamic>).keys,"
         "($expression as Map).values.map(($_closureArg) => $itemSubVal))";
 
-    if (nullable) {
-      result = "$expression == null ? null :" + result;
-    }
-
-    return result;
+    return commonNullPrefix(nullable, expression, result);
   }
 }
 

lib/src/type_helpers/type_helper_utils.dart

@@ -0,0 +1,5 @@
+String commonNullPrefix(
+        bool nullable, String expression, String unsafeExpression) =>
+    nullable
+        ? "$expression == null ? null : $unsafeExpression"
+        : unsafeExpression;

lib/src/utils.dart

@@ -5,14 +5,6 @@
 import 'dart:io';
 import 'package:analyzer/dart/element/element.dart';
 
-String commonNullPrefix(
-    bool nullable, String expression, String unsafeExpression) {
-  if (nullable) {
-    return "$expression == null ? null : $unsafeExpression";
-  }
-  return unsafeExpression;
-}
-
 // Copied from pkg/source_gen - lib/src/utils.
 String friendlyNameForElement(Element element) {
   var friendlyName = element.displayName;