paths = make([]string, len(elem))
	for i, e := range elem {
		paths[i] = pathJoin(prefix, e)
	}
	return paths
}

// string concat alternative to s1 + s2 with low overhead.
func concat(ss ...string) string {
	length := len(ss)
	if length == 0 {
		return ""
	}
	// create & allocate the memory in advance.
	n := 0
	for i := range length {
		n += len(ss[i])

              public void close() throws IOException {
                super.close();
                counter[0]--;
              }
            };
          }
        };
    Reader joinedReader = CharSource.concat(reader, reader, reader).openStream();
    String result = CharStreams.toString(joinedReader);
    assertEquals(testString.length() * 3, result.length());
  }

  public void testReady() throws Exception {

    assertThat(CharSource.concat(ImmutableList.of(c1, c2, c3)).read()).isEqualTo(expected);
    assertThat(CharSource.concat(c1, c2, c3).read()).isEqualTo(expected);
    assertThat(CharSource.concat(ImmutableList.of(c1, c2, c3).iterator()).read())
        .isEqualTo(expected);
    assertFalse(CharSource.concat(c1, c2, c3).isEmpty());

    CharSource emptyConcat = CharSource.concat(CharSource.empty(), CharSource.empty());

    assertArrayEquals(expected, ByteSource.concat(ImmutableList.of(b1, b2, b3)).read());
    assertArrayEquals(expected, ByteSource.concat(b1, b2, b3).read());
    assertArrayEquals(expected, ByteSource.concat(ImmutableList.of(b1, b2, b3).iterator()).read());
    assertEquals(expected.length, ByteSource.concat(b1, b2, b3).size());
    assertFalse(ByteSource.concat(b1, b2, b3).isEmpty());

    assertThat(Bytes.concat()).isEqualTo(EMPTY);
    assertThat(Bytes.concat(EMPTY)).isEqualTo(EMPTY);
    assertThat(Bytes.concat(EMPTY, EMPTY, EMPTY)).isEqualTo(EMPTY);
    assertThat(Bytes.concat(ARRAY1)).isEqualTo(ARRAY1);
    assertThat(Bytes.concat(ARRAY1)).isNotSameInstanceAs(ARRAY1);
    assertThat(Bytes.concat(EMPTY, ARRAY1, EMPTY)).isEqualTo(ARRAY1);
    assertThat(Bytes.concat(ARRAY1, ARRAY1, ARRAY1))

    assertArrayEquals(expected, ByteSource.concat(ImmutableList.of(b1, b2, b3)).read());
    assertArrayEquals(expected, ByteSource.concat(b1, b2, b3).read());
    assertArrayEquals(expected, ByteSource.concat(ImmutableList.of(b1, b2, b3).iterator()).read());
    assertEquals(expected.length, ByteSource.concat(b1, b2, b3).size());
    assertFalse(ByteSource.concat(b1, b2, b3).isEmpty());

      protected Iterator<Integer> newTargetIterator() {
        return Iterators.concat();
      }
    }.test();
  }

  @GwtIncompatible // slow (~5s)
  public void testConcatOneEmptyIteratorYieldsEmpty() {
    new EmptyIteratorTester() {
      @Override
      protected Iterator<Integer> newTargetIterator() {
        return Iterators.concat(iterateOver());
      }
    }.test();
  }

  }

  public void testConcat() {
    assertThat(Doubles.concat()).isEqualTo(EMPTY);
    assertThat(Doubles.concat(EMPTY)).isEqualTo(EMPTY);
    assertThat(Doubles.concat(EMPTY, EMPTY, EMPTY)).isEqualTo(EMPTY);
    assertThat(Doubles.concat(ARRAY1)).isEqualTo(ARRAY1);
    assertThat(Doubles.concat(ARRAY1)).isNotSameInstanceAs(ARRAY1);
    assertThat(Doubles.concat(EMPTY, ARRAY1, EMPTY)).isEqualTo(ARRAY1);

    assertThat(Chars.concat()).isEqualTo(EMPTY);
    assertThat(Chars.concat(EMPTY)).isEqualTo(EMPTY);
    assertThat(Chars.concat(EMPTY, EMPTY, EMPTY)).isEqualTo(EMPTY);
    assertThat(Chars.concat(ARRAY1)).isEqualTo(ARRAY1);
    assertThat(Chars.concat(ARRAY1)).isNotSameInstanceAs(ARRAY1);
    assertThat(Chars.concat(EMPTY, ARRAY1, EMPTY)).isEqualTo(ARRAY1);
    assertThat(Chars.concat(ARRAY1, ARRAY1, ARRAY1))

  public void testConcat() {
    assertThat(Booleans.concat()).isEqualTo(EMPTY);
    assertThat(Booleans.concat(EMPTY)).isEqualTo(EMPTY);
    assertThat(Booleans.concat(EMPTY, EMPTY, EMPTY)).isEqualTo(EMPTY);
    assertThat(Booleans.concat(ARRAY_FALSE)).isEqualTo(ARRAY_FALSE);
    assertThat(Booleans.concat(ARRAY_FALSE)).isNotSameInstanceAs(ARRAY_FALSE);
    assertThat(Booleans.concat(EMPTY, ARRAY_FALSE, EMPTY)).isEqualTo(ARRAY_FALSE);