public static <I, R> Map<I, R> build(R[] values, Function<? super R, ? extends I> indexFunction) {
        Objects.requireNonNull(values, "values");
        return build(Arrays.asList(values), indexFunction);
    }
Builds an index for the given values, using the indexing function.

@param values the values to index
@param indexFunction the index function
@param <I> the index type
@param <R> the actual (value) type
@return the index
helper/src/main/java/me/lucko/helper/utils/Indexing.java