hasEntry matcher needs proper variance declarations

The return type of the hasEntry matcher is invariant on it's type
parameters which prevents javac from inferring compatible types. This
prevents writing

  public void testFoo() {
    Map<String, Number> m = new HashMap<String,Number>();
    Integer foo = new Integer(6);
    m.put("foo", foo);
    MatcherAssert.assertThat(m, Matcher.hasEntry("foo", foo));
  }

instead, you have to write

  MatcherAssert.assertThat(m, Matcher.<String,Number>hasEntry("foo", foo));

or 

  MatcherAssert.assertThat(m, Matcher.hasEntry("foo", (Number)foo));

If the signature for hasEntry were instead

  public static <K,V> Matcher<Map<? super K,? super V>> hasEntry(K k, V v)

the original example would work fine. This same problem likely applies to
other collection matchers like hasItem, hasKey, etc.

Original issue reported on code.google.com by gere...@gmail.com on 7 Jan 2010 at 9:50

arashja / hamcrest

hasEntry matcher needs proper variance declarations #103