Iterable 的自定义匹配器的正确签名是什么？

Question

我正在尝试为具有 Iterable 字段的 class 编写自定义匹配器。我无法找到一种方法来接受任何匹配器 everyItem、hasItem 和 contains - 因为每个 returns 都是一个略有不同的通用类型。执行此操作的最佳方法是什么？

这是一个演示问题的简单示例 - 我怎样才能编译它？我正在使用 Hamcrest 1.3。

import static org.hamcrest.Matchers.contains;
import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.everyItem;
import static org.hamcrest.Matchers.hasItem;
import static org.junit.Assert.assertThat;

import java.util.Collection;

import org.hamcrest.Description;
import org.hamcrest.Matcher;
import org.hamcrest.TypeSafeDiagnosingMatcher;

    public class MatcherExample {

        public static class Band {
            public Collection<Member> getMembers() {
                return null;
            }
        };

        public static class Member {
        };

        public static Matcher<Band> hasMembers(final Matcher<Iterable<Member>> matcher) {
            return new TypeSafeDiagnosingMatcher<Band>() {
                @Override
                public void describeTo(Description description) {
                }

                @Override
                protected boolean matchesSafely(Band item, Description mismatchDescription) {
                    return matcher.matches(item.getMembers());
                }
            };

        }

        public static void main(String[] args) {
            Band band = new Band();
            assertThat(band, hasMembers(everyItem(equalTo(new Member())))); // works with signature Matcher<Iterable<Member>>
            assertThat(band, hasMembers(hasItem(equalTo(new Member()))));   // works with signature Matcher<Iterable<? super Member>>
            assertThat(band, hasMembers(contains(equalTo(new Member()))));  // works with signature Matcher<Iterable<? extends Member>>
        }
    }

Answer 1

非常棘手的问题。只能使其适用于前两个（everyItem 和 hasItem）

public static <M extends Member, B extends Band, I extends Iterable<? super M>> Matcher<B> hasMembers(
        final Matcher<I> matcher) {
    return new TypeSafeDiagnosingMatcher<B>() {
        @Override
        public void describeTo(Description description) {
        }

        @Override
        protected boolean matchesSafely(B item, Description mismatchDescription) {
            return matcher.matches(item.getMembers());
        }
    };
}

Answer 2

以下签名对我有用：

public static Matcher<Band> hasMembers(final Matcher<? super Iterable<Member>> matcher) {
    // ...
}

旁注：

Hamcrest 具有 FeatureMatcher class 可以轻松地为特定属性创建匹配器：

public static Matcher<Band> hasMembers(final Matcher<? super Iterable<Member>> matcher) {
    return new FeatureMatcher<Band, Iterable<Member>>(matcher, "a band with members", "members") {

        @Override
        protected Iterable<Member> featureValueOf(Band actual) {
            return actual.getMembers();
        }
    };
};

Iterable 的自定义匹配器的正确签名是什么？

What's the right signature for a custom matcher for an Iterable?

java

generics

hamcrest

matcher