How use matchers for collection with Hamcrest?

Question

The input:

1. Collection with MyElement without equals method.
2. A org.hamcrest.TypeSafeMatcher implementation, which matches element by some field.

The goal is make following statement compilable:

Collection<MyElement> elements = ...
Collection<TypeSafeMatchert> matchers = ...
assertThat(elements, Matchers.contains(matchers); //<error here

What have to use here? It wants me to Matcher<? super java.util.List<MyElement>> Matcher<? super java.util.List<MyElement>> and told that actully I passed Matcher<java.lang.Iterable<? super java.util.List<MyElement>>> Matcher<java.lang.Iterable<? super java.util.List<MyElement>>> . So how to pass a Matcher Collection here?

There is a question about comparing collections with hamcrest, but there is no example with passing Matchers collection, not elements.

Answer 1

Use List instead of collection for the matchers, or convert it to array.

Hamcrest has following contains methods:

public static <E> org.hamcrest.Matcher<java.lang.Iterable<? extends E>> contains(org.hamcrest.Matcher<? super E>... itemMatchers)

public static <E> org.hamcrest.Matcher<java.lang.Iterable<? extends E>> contains(E... items)

public static <E> org.hamcrest.Matcher<java.lang.Iterable<? extends E>> contains(org.hamcrest.Matcher<? super E> itemMatcher)

public static <E> org.hamcrest.Matcher<java.lang.Iterable<? extends E>> contains(java.util.List<org.hamcrest.Matcher<? super E>> itemMatchers)

As you can see it handles Matchers only in case of a List or varags (but if you pass only one element then you need to convert it to array).

Answer 2

Instead of defining a Collection of TypeSafeMatchers , you need to define a:

    List<Matcher<? super MyElement>> matchers = ...;

This way, Hamcrest will know what you want.