feature(Matcher): add type param to Matcher for item in functions

Eliminates 4 errors when `implicit-casts: false` is set

Author: kevmoo

CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.12.3
+
+- Add type parameters to `Matcher` class to specify the type of `item` in
+  `matches` and `describeMismatch` functions.
+
 ## 0.12.2+1
 
 - Updated SDK version to 2.0.0-dev.17.0

lib/src/core_matchers.dart

@@ -69,13 +69,13 @@ const Matcher isNaN = const _IsNaN();
 /// A matcher that matches any non-NaN value.
 const Matcher isNotNaN = const _IsNotNaN();
 
-class _IsNaN extends Matcher {
+class _IsNaN extends Matcher<num> {
   const _IsNaN();
   bool matches(item, Map matchState) => double.nan.compareTo(item) == 0;
   Description describe(Description description) => description.add('NaN');
 }
 
-class _IsNotNaN extends Matcher {
+class _IsNotNaN extends Matcher<num> {
   const _IsNotNaN();
   bool matches(item, Map matchState) => double.nan.compareTo(item) != 0;
   Description describe(Description description) => description.add('not NaN');

lib/src/custom_matcher.dart

@@ -30,7 +30,7 @@ import 'util.dart';
 /// ```dart
 /// expect(inventoryItem, new HasPrice(greaterThan(0)));
 /// ```
-class CustomMatcher extends Matcher {
+class CustomMatcher<T> extends Matcher<T> {
   final String _featureDescription;
   final String _featureName;
   final Matcher _matcher;
@@ -39,9 +39,9 @@ class CustomMatcher extends Matcher {
       : this._matcher = wrapMatcher(matcher);
 
   /// Override this to extract the interesting feature.
-  Object featureValueOf(actual) => actual;
+  Object featureValueOf(T actual) => actual;
 
-  bool matches(item, Map matchState) {
+  bool matches(T item, Map matchState) {
     try {
       var f = featureValueOf(item);
       if (_matcher.matches(f, matchState)) return true;

lib/src/equals_matcher.dart

@@ -19,7 +19,7 @@ typedef _RecursiveMatcher = List<String> Function(
     dynamic, dynamic, String, int);
 
 /// A special equality matcher for strings.
-class _StringEqualsMatcher extends Matcher {
+class _StringEqualsMatcher extends Matcher<String> {
   final String _value;
 
   _StringEqualsMatcher(this._value);

lib/src/interfaces.dart

@@ -31,14 +31,14 @@ abstract class Description {
 /// so this does not need to be provided unless a more clear description is
 /// required. The other two methods ([matches] and [describe])
 /// must always be provided as they are highly matcher-specific.
-abstract class Matcher {
+abstract class Matcher<T> {
   const Matcher();
 
   /// This does the matching of the actual vs expected values.
   /// [item] is the actual value. [matchState] can be supplied
   /// and may be used to add details about the mismatch that are too
   /// costly to determine in [describeMismatch].
-  bool matches(item, Map matchState);
+  bool matches(T item, Map matchState);
 
   /// This builds a textual description of the matcher.
   Description describe(Description description);
@@ -51,7 +51,7 @@ abstract class Matcher {
   /// A few matchers make use of the [verbose] flag to provide detailed
   /// information that is not typically included but can be of help in
   /// diagnosing failures, such as stack traces.
-  Description describeMismatch(item, Description mismatchDescription,
+  Description describeMismatch(T item, Description mismatchDescription,
           Map matchState, bool verbose) =>
       mismatchDescription;
 }

lib/src/iterable_matchers.dart

@@ -130,7 +130,7 @@ class _UnorderedEquals extends _UnorderedMatches {
 
 /// Iterable matchers match against [Iterable]s. We add this intermediate
 /// class to give better mismatch error messages than the base Matcher class.
-abstract class _IterableMatcher extends Matcher {
+abstract class _IterableMatcher extends Matcher<Iterable> {
   const _IterableMatcher();
   Description describeMismatch(
       item, Description mismatchDescription, Map matchState, bool verbose) {

test/custom_matcher_test.dart

@@ -12,9 +12,9 @@ class _BadCustomMatcher extends CustomMatcher {
   Object featureValueOf(actual) => throw new Exception("bang");
 }
 
-class _HasPrice extends CustomMatcher {
+class _HasPrice extends CustomMatcher<Widget> {
   _HasPrice(matcher) : super("Widget with a price that is", "price", matcher);
-  Object featureValueOf(actual) => actual.price;
+  Object featureValueOf(Widget actual) => actual.price;
 }
 
 void main() {