Varargs methods produce warnings for generic parameters #132

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orionll opened this Issue Dec 12, 2012 · 2 comments

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@orionll
List<Integer> list1 = new ArrayList<Integer>();
List<Integer> list2 = new ArrayList<Integer>();
List<Integer> list3 = new ArrayList<Integer>();

List<List<Integer>> listOfLists = new ArrayList<List<Integer>>();
listOfLists.add(list1);
listOfLists.add(list2);
listOfLists.add(list3);

assertThat(listOfLists).contains(list1, list2, list3); // Type safety: A generic array of List<Integer> is created for a varargs parameter

This problem can be solved by overloading a varargs method with a different number of arguments:

public S contains(T value1) { ... }
public S contains(T value1, T value2) { ... }
public S contains(T value1, T value2, T value3) { ... }
public S contains(T value1, T value2, T value3, T value4) { ... }
...

This technique is used, for example, in Guava: http://code.google.com/p/guava-libraries/source/browse/guava/src/com/google/common/collect/ImmutableList.java

@alexruiz
Owner

The problem is that the vararg takes an array of T, where it should just an array of Object. For tests it really doesn't matter type safety in the vararg. A failing test will tell the user that something is wrong.

@alexruiz alexruiz was assigned Jan 10, 2013
@mjball

Wouldn't adding a @SafeVarargs annotation suffice?

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