diff --git a/CMakeLists.txt b/CMakeLists.txt
index 42e5fcd..ab1514f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -44,7 +44,7 @@ set(HEADER_FILES
   src/Vector.hpp
   src/xcdat_basics.hpp
   src/xcdat_config.hpp
-  )
+  src/xcdat.hpp)
 
 set(SOURCE_FILES
   src/BitVector.cpp
@@ -61,7 +61,7 @@ set_target_properties(xcdat-exe PROPERTIES OUTPUT_NAME xcdat)
 target_link_libraries(xcdat-exe xcdat)
 
 enable_testing()
-file(GLOB TEST_SOURCES src/test*.cpp)
+file(GLOB TEST_SOURCES src/*_test.cpp)
 foreach(TEST_SOURCE ${TEST_SOURCES})
   get_filename_component(TEST_SOURCE_NAME ${TEST_SOURCE} NAME_WE)
   add_executable(${TEST_SOURCE_NAME} ${TEST_SOURCE})
diff --git a/src/BitVector.cpp b/src/BitVector.cpp
index 86f640b..8c86eca 100644
--- a/src/BitVector.cpp
+++ b/src/BitVector.cpp
@@ -234,13 +234,13 @@ BitVector::BitVector(BitVectorBuilder& builder, bool rank_flag,
   }
 }
 
-id_type BitVector::rank(size_t i) const {
+id_type BitVector::rank(id_type i) const {
   auto& hint = rank_tips_[i / kBitsInR1];
   return hint.L1 + hint.L2[i / kBitsInR2 % kR1PerR2]
          + pop_count(bits_[i / 32] & ((1U << (i % 32)) - 1));
 }
 
-id_type BitVector::select(size_t i) const {
+id_type BitVector::select(id_type i) const {
   id_type left = 0, right = static_cast<id_type>(rank_tips_.size());
 
   if (!select_tips_.is_empty()) {
diff --git a/src/BitVector.hpp b/src/BitVector.hpp
index 8636bed..e8c9bb0 100644
--- a/src/BitVector.hpp
+++ b/src/BitVector.hpp
@@ -10,20 +10,19 @@ namespace xcdat {
 class BitVector {
 public:
   BitVector() = default;
-  ~BitVector() = default;
-
   explicit BitVector(std::istream &is);
-  explicit BitVector(BitVectorBuilder& builder,
-                     bool rank_flag, bool select_flag);
+  BitVector(BitVectorBuilder& builder, bool rank_flag, bool select_flag);
+
+  ~BitVector() = default;
 
   bool operator[](size_t i) const {
     return (bits_[i / 32] & (1U << (i % 32))) != 0;
   }
 
   // the number of 1s in B[0,i).
-  id_type rank(size_t i) const;
+  id_type rank(id_type i) const;
   // the position of the i+1 th occurrence.
-  id_type select(size_t i) const;
+  id_type select(id_type i) const;
 
   size_t num_1s() const {
     return num_1s_;
diff --git a/src/FastDacBc.cpp b/src/FastDacBc.cpp
index c77e24a..f11c88f 100644
--- a/src/FastDacBc.cpp
+++ b/src/FastDacBc.cpp
@@ -17,7 +17,8 @@ FastDacBc::FastDacBc(std::istream& is) {
   num_free_nodes_ = read_value<size_t>(is);
 }
 
-FastDacBc::FastDacBc(const std::vector<BcPair>& bc, BitVectorBuilder& leaf_flags) {
+FastDacBc::FastDacBc(const std::vector<BcPair>& bc,
+                     BitVectorBuilder& leaf_flags) {
   if (bc.empty()) {
     return;
   }
diff --git a/src/FastDacBc.hpp b/src/FastDacBc.hpp
index d7b5691..5bde871 100644
--- a/src/FastDacBc.hpp
+++ b/src/FastDacBc.hpp
@@ -70,16 +70,16 @@ public:
   FastDacBc& operator=(FastDacBc&&) noexcept = default;
 
 private:
-  Vector<uint8_t> values_L1_ {};
-  Vector<uint16_t> values_L2_ {};
-  Vector<uint32_t> values_L3_ {};
+  Vector <uint8_t> values_L1_{};
+  Vector <uint16_t> values_L2_{};
+  Vector <uint32_t> values_L3_{};
 #ifdef XCDAT_X64
   Vector<uint64_t> values_L4_ {};
 #endif
-  Vector<id_type> ranks_[kLayers - 1] {};
-  BitVector leaf_flags_ {};
-  FitVector links_ {};
-  size_t num_free_nodes_ {};
+  Vector <id_type> ranks_[kLayers - 1]{};
+  BitVector leaf_flags_{};
+  FitVector links_{};
+  size_t num_free_nodes_{};
 
   id_type access_(id_type i) const;
 };
diff --git a/src/TrieBuilder.cpp b/src/TrieBuilder.cpp
index 22a4097..2248a52 100644
--- a/src/TrieBuilder.cpp
+++ b/src/TrieBuilder.cpp
@@ -3,8 +3,10 @@
 
 namespace xcdat {
 
-TrieBuilder::TrieBuilder(const std::vector<Key>& keys, id_type width_L1, bool binary_mode)
-  : keys_(keys), block_size_(1U << width_L1), width_L1_(width_L1), binary_mode_(binary_mode) {
+TrieBuilder::TrieBuilder(const std::vector<Key>& keys,
+                         id_type width_L1, bool binary_mode)
+  : keys_(keys), block_size_(1U << width_L1), width_L1_(width_L1),
+    binary_mode_(binary_mode) {
   if (keys_.empty()) {
     throw TrieBuilder::Exception("The input data is empty.");
   }
@@ -13,16 +15,16 @@ TrieBuilder::TrieBuilder(const std::vector<Key>& keys, id_type width_L1, bool bi
   }
 
   {
-    size_t init_capacity = 1;
-    while (init_capacity < keys_.size()) {
-      init_capacity <<= 1;
+    size_t init_capa = 1;
+    while (init_capa < keys_.size()) {
+      init_capa <<= 1;
     }
 
-    bc_.reserve(init_capacity);
-    leaf_flags_.reserve(init_capacity);
-    term_flags_.reserve(init_capacity);
-    used_flags_.reserve(init_capacity);
-    heads_.reserve(init_capacity >> width_L1_);
+    bc_.reserve(init_capa);
+    leaf_flags_.reserve(init_capa);
+    term_flags_.reserve(init_capa);
+    used_flags_.reserve(init_capa);
+    heads_.reserve(init_capa >> width_L1_);
   }
 
   alphabet_.reserve(256);
@@ -94,7 +96,8 @@ void TrieBuilder::build_table_() {
   }
 }
 
-void TrieBuilder::build_bc_(size_t begin, size_t end, size_t depth, id_type node_id) {
+void TrieBuilder::build_bc_(size_t begin, size_t end, size_t depth,
+                            id_type node_id) {
   if (keys_[begin].length == depth) {
     term_flags_.set_bit(node_id, true);
     if (++begin == end) { // without link?
@@ -117,7 +120,9 @@ void TrieBuilder::build_bc_(size_t begin, size_t end, size_t depth, id_type node
       const auto _label = keys_[str_id].ptr[depth];
       if (label != _label) {
         if (_label < label) {
-          throw TrieBuilder::Exception("The input data is not in lexicographical order.");
+          throw TrieBuilder::Exception(
+            "The input data is not in lexicographical order."
+          );
         }
         edges_.push_back(label);
         label = _label;
@@ -177,13 +182,16 @@ void TrieBuilder::build_tail_() {
     }
 
     size_t match = 0;
-    while ((match < cur.length()) && (match < prev->length()) && ((*prev)[match] == cur[match])) {
+    while ((match < cur.length()) && (match < prev->length())
+           && ((*prev)[match] == cur[match])) {
       ++match;
     }
 
     if ((match == cur.length()) && (prev->length() != 0)) { // sharing
       bc_[cur.node_id].base =
-        static_cast<id_type>(bc_[prev->node_id].base + (prev->length() - match));
+        static_cast<id_type>(
+          bc_[prev->node_id].base + (prev->length() - match)
+        );
     } else { // append
       bc_[cur.node_id].base = static_cast<id_type>(tail_.size());
       for (size_t j = 0; j < cur.length(); ++j) {
@@ -276,7 +284,8 @@ id_type TrieBuilder::find_base_(id_type block_id) const {
   }
 
   // search in the same block
-  for (auto i = heads_[block_id]; i != kTabooId && i >> width_L1_ == block_id; i = bc_[i].base) {
+  for (auto i = heads_[block_id]; i != kTabooId && i >> width_L1_ == block_id;
+       i = bc_[i].base) {
     const auto base = i ^ table_[edges_[0]];
     if (is_target_(base)) {
       return base; // base / block_size_ == block_id
diff --git a/src/TrieBuilder.hpp b/src/TrieBuilder.hpp
index 291a2a1..d0dab68 100644
--- a/src/TrieBuilder.hpp
+++ b/src/TrieBuilder.hpp
@@ -23,13 +23,13 @@ public:
   // reported by TrieBuilder::Exception. If the keys include the ASCII zero
   // code, pass binary_mode = true.
   template<bool Fast>
-  static Trie<Fast> build(const std::vector<Key>& keys,
-                          bool binary_mode = false) {
-    TrieBuilder builder(keys, Trie<Fast>::BcType::kWidthL1, binary_mode);
+  static Trie<Fast>
+  build(const std::vector<Key>& keys, bool binary_mode = false) {
+    TrieBuilder builder(keys, Trie<Fast>::bc_type::kWidthL1, binary_mode);
 
     Trie<Fast> trie;
 
-    trie.bc_ = typename Trie<Fast>::BcType(builder.bc_, builder.leaf_flags_);
+    trie.bc_ = typename Trie<Fast>::bc_type(builder.bc_, builder.leaf_flags_);
     trie.terminal_flags_ = BitVector(builder.term_flags_, true, true);
     trie.tail_ = Vector<uint8_t>(builder.tail_);
     trie.boundary_flags_ = BitVector(builder.boundary_flags_, false, false);
@@ -85,22 +85,22 @@ private:
   const id_type block_size_;
   const id_type width_L1_;
 
-  bool binary_mode_ {};
+  bool binary_mode_{};
 
-  std::vector<BcPair> bc_ {};
-  BitVectorBuilder leaf_flags_ {};
-  BitVectorBuilder term_flags_ {};
-  std::vector<uint8_t> tail_ {};
-  BitVectorBuilder boundary_flags_ {};
-  std::vector<uint8_t> alphabet_ {};
-  uint8_t table_[512] {};
+  std::vector<BcPair> bc_{};
+  BitVectorBuilder leaf_flags_{};
+  BitVectorBuilder term_flags_{};
+  std::vector<uint8_t> tail_{};
+  BitVectorBuilder boundary_flags_{};
+  std::vector<uint8_t> alphabet_{};
+  uint8_t table_[512]{};
 
-  std::vector<bool> used_flags_ {};
-  std::vector<uint8_t> edges_ {};
-  std::vector<id_type> heads_ {};
-  std::vector<Suffix> suffixes_ {};
+  std::vector<bool> used_flags_{};
+  std::vector<uint8_t> edges_{};
+  std::vector<id_type> heads_{};
+  std::vector<Suffix> suffixes_{};
 
-  size_t max_length_ {};
+  size_t max_length_{};
 
   TrieBuilder(const std::vector<Key>& keys, id_type width_L1, bool binary_mode);
   ~TrieBuilder() = default;
diff --git a/src/tries_test.cpp b/src/tries_test.cpp
index 3bb79bc..939eb73 100644
--- a/src/tries_test.cpp
+++ b/src/tries_test.cpp
@@ -6,7 +6,7 @@
 #include <random>
 #include <cstring>
 
-#include "TrieBuilder.hpp"
+#include "xcdat.hpp"
 
 using namespace xcdat;
 
@@ -75,7 +75,7 @@ void test_basic_operations(const Trie<Fast>& trie, const std::vector<Key>& keys,
 
   for (auto& key : keys) {
     const auto id = trie.lookup(key.ptr, key.length);
-    assert(id != NOT_FOUND);
+    assert(id != kNotFound);
 
     std::vector<uint8_t> ret;
     trie.access(id, ret);
@@ -86,7 +86,7 @@ void test_basic_operations(const Trie<Fast>& trie, const std::vector<Key>& keys,
 
   for (auto& other : others) {
     const auto id = trie.lookup(other.ptr, other.length);
-    assert(id == NOT_FOUND);
+    assert(id == kNotFound);
   }
 }
 
@@ -96,44 +96,48 @@ void test_prefix_operations(const Trie<Fast>& trie, const std::vector<Key>& keys
   std::cerr << "Prefix operations -> common_prefix_lookup()" << std::endl;
 
   for (auto& key : keys) {
-    std::vector<id_type> ids;
-    auto num_ids = trie.common_prefix_lookup(key.ptr, key.length, ids);
+    size_t num_results = 0;
 
-    assert(1 <= num_ids);
-    assert(num_ids <= kMaxLength);
-    assert(num_ids == ids.size());
+    auto it = trie.make_prefix_iterator(key.ptr, key.length);
+    while (it.next()) {
+      auto id = it.id();
+      auto dec = it.key();
 
-    for (auto id : ids) {
-      std::vector<uint8_t> ret;
-      trie.access(id, ret);
-      assert(ret.size() <= key.length);
+      assert(dec.second <= key.length);
+
+      std::vector<uint8_t> dec2;
+      trie.access(id, dec2);
+
+      assert(dec.second == dec2.size());
+      assert(std::memcmp(dec.first, dec2.data(), dec.second) == 0);
+
+      ++num_results;
     }
 
-    auto limit = num_ids / 2;
-    auto new_num_ids = trie.common_prefix_lookup(key.ptr, key.length, ids, limit);
-
-    assert(new_num_ids == limit);
-    assert(num_ids + new_num_ids == ids.size());
+    assert(1 <= num_results);
+    assert(num_results <= key.length);
   }
 
   for (auto& other : others) {
-    std::vector<id_type> ids;
-    auto num_ids = trie.common_prefix_lookup(other.ptr, other.length, ids);
+    size_t num_results = 0;
 
-    assert(num_ids <= kMaxLength);
-    assert(num_ids == ids.size());
+    auto it = trie.make_prefix_iterator(other.ptr, other.length);
+    while (it.next()) {
+      auto id = it.id();
+      auto dec = it.key();
 
-    for (auto id : ids) {
-      std::vector<uint8_t> ret;
-      trie.access(id, ret);
-      assert(ret.size() < other.length);
+      assert(dec.second < other.length);
+
+      std::vector<uint8_t> dec2;
+      trie.access(id, dec2);
+
+      assert(dec.second == dec2.size());
+      assert(std::memcmp(dec.first, dec2.data(), dec.second) == 0);
+
+      ++num_results;
     }
 
-    auto limit = num_ids / 2;
-    auto new_num_ids = trie.common_prefix_lookup(other.ptr, other.length, ids, limit);
-
-    assert(new_num_ids == limit);
-    assert(num_ids + new_num_ids == ids.size());
+    assert(num_results < other.length);
   }
 }
 
@@ -143,42 +147,63 @@ void test_predictive_operations(const Trie<Fast>& trie, const std::vector<Key>&
   std::cerr << "Predictive operations -> predictive_lookup()" << std::endl;
 
   for (auto& key : keys) {
-    std::vector<id_type> ids;
-    auto num_ids = trie.predictive_lookup(key.ptr, key.length, ids);
+    size_t num_results = 0;
 
-    assert(1 <= num_ids);
-    assert(num_ids == ids.size());
+    auto it = trie.make_predictive_iterator(key.ptr, key.length);
+    while (it.next()) {
+      auto id = it.id();
+      auto dec = it.key();
 
-    for (auto id : ids) {
-      std::vector<uint8_t> ret;
-      trie.access(id, ret);
-      assert(key.length <= ret.size());
+      assert(key.length <= dec.second);
+
+      std::vector<uint8_t> dec2;
+      trie.access(id, dec2);
+
+      assert(dec.second == dec2.size());
+      assert(std::memcmp(dec.first, dec2.data(), dec.second) == 0);
+
+      ++num_results;
     }
 
-    auto limit = num_ids / 2;
-    auto new_num_ids = trie.predictive_lookup(key.ptr, key.length, ids, limit);
-
-    assert(new_num_ids == limit);
-    assert(num_ids + new_num_ids == ids.size());
+    assert(1 <= num_results);
   }
 
   for (auto& other : others) {
-    std::vector<id_type> ids;
-    auto num_ids = trie.predictive_lookup(other.ptr, other.length, ids);
+    auto it = trie.make_predictive_iterator(other.ptr, other.length);
+    while (it.next()) {
+      auto id = it.id();
+      auto dec = it.key();
 
-    assert(num_ids == ids.size());
+      assert(other.length < dec.second);
 
-    for (auto id : ids) {
-      std::vector<uint8_t> ret;
-      trie.access(id, ret);
-      assert(other.length < ret.size());
+      std::vector<uint8_t> dec2;
+      trie.access(id, dec2);
+
+      assert(dec.second == dec2.size());
+      assert(std::memcmp(dec.first, dec2.data(), dec.second) == 0);
+    }
+  }
+
+  { // all enumeration
+    size_t num_results = 0;
+
+    auto it = trie.make_predictive_iterator(nullptr, 0);
+    while (it.next()) {
+      auto id = it.id();
+      auto dec = it.key();
+
+      assert(0 <= dec.second);
+
+      std::vector<uint8_t> dec2;
+      trie.access(id, dec2);
+
+      assert(dec.second == dec2.size());
+      assert(std::memcmp(dec.first, dec2.data(), dec.second) == 0);
+
+      ++num_results;
     }
 
-    auto limit = num_ids / 2;
-    auto new_num_ids = trie.predictive_lookup(other.ptr, other.length, ids, limit);
-
-    assert(new_num_ids == limit);
-    assert(num_ids + new_num_ids == ids.size());
+    assert(num_results == trie.num_keys());
   }
 }
 
diff --git a/src/xcdat.cpp b/src/xcdat.cpp
index 410eca6..553c513 100644
--- a/src/xcdat.cpp
+++ b/src/xcdat.cpp
@@ -2,7 +2,7 @@
 #include <iostream>
 #include <random>
 
-#include "TrieBuilder.hpp"
+#include "xcdat.hpp"
 
 using namespace xcdat;
 
@@ -143,8 +143,8 @@ int query(std::vector<std::string>& args) {
   }
 
   std::string query;
-  std::vector<id_type> ids;
-  std::vector<uint8_t> buf;
+//  std::vector<id_type> ids;
+//  std::vector<uint8_t> buf;
 
   while (true){
     putchar('>');
@@ -165,29 +165,47 @@ int query(std::vector<std::string>& args) {
     }
 
     std::cout << "common_prefix_lookup()" << std::endl;
-    ids.clear();
-    trie.common_prefix_lookup(key, length, ids);
-    std::cout << ids.size() << " found" << std::endl;
+    {
+      size_t N = 0;
+      auto it = trie.make_prefix_iterator(key, length);
+      while (N < limit && it.next()) {
+        std::cout << it.id() << '\t';
+        std::cout.write(reinterpret_cast<const char*>(it.key().first), it.key().second);
+        std::cout << std::endl;
+        ++N;
+      }
 
-    for (size_t i = 0; i < std::min(ids.size(), limit); ++i) {
-      buf.clear();
-      trie.access(ids[i], buf);
-      std::cout << ids[i] << '\t';
-      std::cout.write(reinterpret_cast<const char*>(buf.data()), buf.size());
-      std::cout << std::endl;
+      size_t M = 0;
+      while (it.next()) {
+        ++M;
+      }
+
+      if (M != 0) {
+        std::cout << "and more..." << std::endl;
+      }
+      std::cout << N + M << " found" << std::endl;
     }
 
     std::cout << "predictive_lookup()" << std::endl;
-    ids.clear();
-    trie.predictive_lookup(key, length, ids);
-    std::cout << ids.size() << " found" << std::endl;
+    {
+      size_t N = 0;
+      auto it = trie.make_predictive_iterator(key, length);
+      while (N < limit && it.next()) {
+        std::cout << it.id() << '\t';
+        std::cout.write(reinterpret_cast<const char*>(it.key().first), it.key().second);
+        std::cout << std::endl;
+        ++N;
+      }
 
-    for (size_t i = 0; i < std::min(ids.size(), limit); ++i) {
-      buf.clear();
-      trie.access(ids[i], buf);
-      std::cout << ids[i] << '\t';
-      std::cout.write(reinterpret_cast<const char*>(buf.data()), buf.size());
-      std::cout << std::endl;
+      size_t M = 0;
+      while (it.next()) {
+        ++M;
+      }
+
+      if (M != 0) {
+        std::cout << "and more..." << std::endl;
+      }
+      std::cout << N + M << " found" << std::endl;
     }
   }
 
diff --git a/src/xcdat.hpp b/src/xcdat.hpp
index 7a46575..c173ce4 100644
--- a/src/xcdat.hpp
+++ b/src/xcdat.hpp
@@ -5,4 +5,13 @@
 #ifndef XCDAT_XCDAT_HPP
 #define XCDAT_XCDAT_HPP
 
+#include "TrieBuilder.hpp"
+
+namespace xcdat {
+
+
+
+}
+
+
 #endif //XCDAT_XCDAT_HPP