diff --git a/API.md b/API.md
index 5f1731a..8e127d2 100644
--- a/API.md
+++ b/API.md
@@ -1,5 +1,5 @@
 # Supported API
-## Implemented 7% (20/259)
+## Implemented 8% (22/259)
 ### Database (2 / 24)
 
 |Command                                              |impl|test|note|
@@ -47,21 +47,21 @@
 |`rocksdb_multi_get`   |    |    |    |
 |`rocksdb_multi_get_cf`|    |    |    |
 
-### Iteration (8 / 12)
+### Iteration (10 / 12)
 
 |Command                     |impl|test|note|
 |----------------------------|:--:|:--:|----|
-|`rocksdb_create_iterator`   |  ✓ |    |    |
+|`rocksdb_create_iterator`   |  ✓ |  ✓ |    |
 |`rocksdb_create_iterator_cf`|    |    |    |
-|`rocksdb_iter_destroy`      |  ✓ |    |    |
-|`rocksdb_iter_valid`        |  ✓ |    |    |
-|`rocksdb_iter_seek_to_first`|  ✓ |    |    |
-|`rocksdb_iter_seek_to_last` |  ✓ |    |    |
-|`rocksdb_iter_seek`         |    |    |    |
-|`rocksdb_iter_next`         |  ✓ |    |    |
-|`rocksdb_iter_prev`         |  ✓ |    |    |
-|`rocksdb_iter_key`          |  ✓ |    |    |
-|`rocksdb_iter_value`        |    |    |    |
+|`rocksdb_iter_destroy`      |  ✓ |  ✓ |    |
+|`rocksdb_iter_valid`        |  ✓ |  ✓ |    |
+|`rocksdb_iter_seek_to_first`|  ✓ |  ✓ |    |
+|`rocksdb_iter_seek_to_last` |  ✓ |  ✓ |    |
+|`rocksdb_iter_seek`         |  ✓ |  ✓ |    |
+|`rocksdb_iter_next`         |  ✓ |  ✓ |    |
+|`rocksdb_iter_prev`         |  ✓ |  ✓ |    |
+|`rocksdb_iter_key`          |  ✓ |  ✓ |    |
+|`rocksdb_iter_value`        |  ✓ |  ✓ |    |
 |`rocksdb_iter_get_error`    |    |    |    |
 
 ### Snapshots (0 / 15)
diff --git a/Makefile b/Makefile
index f80dd24..62ea07f 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 API_IMPLS := src/rocksdb/api.cr
 OPT_IMPLS := src/rocksdb/options.cr
-CMD_TESTS := $(shell find spec/commands -name '*.cr')
+CMD_TESTS := $(shell find spec -name '*_spec.cr')
 API_FILES := $(shell find doc/api -name '*.*')
 
 .PHONY : all
diff --git a/README.md b/README.md
index 7aede6c..c78b7ec 100644
--- a/README.md
+++ b/README.md
@@ -36,12 +36,44 @@ db.get("foo")      # => ""
 db.get?("foo")     # => nil
 db.get!("foo")     # raise RocksDB::NotFound.new("foo")
 
-db.keys            # => ["k1","k2","k3",...]
-db.keys(2)         # => ["k1","k2"]
-
 db.close
 ```
 
+### Iterations
+
+```shell
+3.times{|i| db.put("k#{i}", i) }
+db.keys            # => ["k0","k1","k2"]
+db.keys(2)         # => ["k0","k1"]
+
+db.each do |(k,v)|
+```
+
+### Iterator
+
+```shell
+iter = db.new_iterator
+iter.key           # => "k0"
+iter.next
+iter.value         # => "1"
+iter.first
+iter.key           # => "k0"
+iter.seek("k2")
+iter.next
+iter.valid?        # => false
+```
+
+- same as `each`
+
+```shell
+iter = db.new_iterator
+iter.first
+while (iter.valid?)
+  # yield {iter.key, iter.value}
+  iter.next
+end  
+```
+
 ### binary data
 
 Although all data are stored as Binary in RocksDB,
@@ -57,8 +89,12 @@ db.get("\u{0}")   # => "\t"
 
 #### 0.3.0
 
-- [x] `keys`
-- [ ] `each`
+- [x] `keys` (String)
+- [x] `each` (String)
+
+#### 0.4.0
+
+- [ ] Iterations for Binary
 
 ## Testing
 
diff --git a/doc/api/impl b/doc/api/impl
index 2462f85..428c5d9 100644
--- a/doc/api/impl
+++ b/doc/api/impl
@@ -6,9 +6,11 @@ rocksdb_iter_destroy
 rocksdb_iter_key
 rocksdb_iter_next
 rocksdb_iter_prev
+rocksdb_iter_seek
 rocksdb_iter_seek_to_first
 rocksdb_iter_seek_to_last
 rocksdb_iter_valid
+rocksdb_iter_value
 rocksdb_open
 rocksdb_options_create
 rocksdb_options_destroy
diff --git a/doc/api/test b/doc/api/test
index 41f7527..b14ab1a 100644
--- a/doc/api/test
+++ b/doc/api/test
@@ -1,7 +1,18 @@
 each
 keys
+new_iterator
 rocksdb_close
+rocksdb_create_iterator
 rocksdb_delete
 rocksdb_get
+rocksdb_iter_destroy
+rocksdb_iter_key
+rocksdb_iter_next
+rocksdb_iter_prev
+rocksdb_iter_seek
+rocksdb_iter_seek_to_first
+rocksdb_iter_seek_to_last
+rocksdb_iter_valid
+rocksdb_iter_value
 rocksdb_open
 rocksdb_put
diff --git a/spec/commands/iteration_spec.cr b/spec/commands/iteration_spec.cr
index 5fd8397..5fa05f4 100644
--- a/spec/commands/iteration_spec.cr
+++ b/spec/commands/iteration_spec.cr
@@ -1,17 +1,17 @@
 require "../spec_helper"
 
 describe "Iterations" do
-  path = "tmp/db_iter"
+  path = "tmp/db_iteration"
 
   it "(setup)" do
     db = RocksDB::DB.new(path)
-    5.times{|i| db.put("k#{i}", i) }
+    3.times{|i| db.put("k#{i}", i) }
     db.close
   end
   
   it "#keys" do
     db = RocksDB::DB.new(path)
-    db.keys.should eq(%w( k0 k1 k2 k3 k4 ))
+    db.keys.should eq(%w( k0 k1 k2 ))
     db.close
   end
 
@@ -23,12 +23,19 @@ describe "Iterations" do
 
   it "#each" do
     db = RocksDB::DB.new(path)
+    items = [] of Tuple(String, String)
+    db.each do |k,v|
+      items << {k, v}
+    end
+    items.should eq([{"k0", "0"}, {"k1", "1"}, {"k2", "2"}])
+    db.close
+  end
 
-#    items = [] of Tuple(String, String)
-#    db.each do |k,v|
-#      items << {k, v}
-#    end
-      
+  it "#new_iterator" do
+    db = RocksDB::DB.new(path)
+    iter = db.new_iterator
+    iter.should be_a(RocksDB::Iterator)
+    iter.close
     db.close
   end
 end
diff --git a/spec/iterator_spec.cr b/spec/iterator_spec.cr
new file mode 100644
index 0000000..b166f40
--- /dev/null
+++ b/spec/iterator_spec.cr
@@ -0,0 +1,61 @@
+require "./spec_helper"
+
+describe "Iterator" do
+  path = "tmp/db_iteration"
+
+  it "work" do
+    db = RocksDB::DB.new(path)
+    3.times{|i| db.put("k#{i}", i) }
+    iter = RocksDB::Iterator.new(db)
+
+    iter.valid?.should be_false
+    
+    iter.first
+    iter.valid?.should be_true
+    iter.key.should eq("k0")
+    iter.value.should eq("0")
+
+    iter.next
+    iter.key.should eq("k1")
+    iter.value.should eq("1")
+
+    iter.next
+    iter.key.should eq("k2")
+    iter.value.should eq("2")
+
+    iter.prev
+    iter.key.should eq("k1")
+    iter.value.should eq("1")
+
+    iter.first
+    iter.key.should eq("k0")
+    iter.value.should eq("0")
+
+    iter.last
+    iter.key.should eq("k2")
+    iter.value.should eq("2")
+
+    iter.next
+    iter.valid?.should be_false
+
+    iter.seek("k1")
+    iter.valid?.should be_true
+    iter.key.should eq("k1")
+
+    iter.seek("xx")
+    iter.valid?.should be_false
+    
+    db.close
+  end
+
+  it "#rocksdb_create_iterator" do ; end
+  it "#rocksdb_iter_destroy" do ; end
+  it "#rocksdb_iter_seek_to_first" do ; end
+  it "#rocksdb_iter_seek_to_last" do ; end
+  it "#rocksdb_iter_seek" do; end
+  it "#rocksdb_iter_prev" do; end
+  it "#rocksdb_iter_next" do; end
+  it "#rocksdb_iter_key" do; end
+  it "#rocksdb_iter_value" do ; end
+  it "#rocksdb_iter_valid" do ; end
+end
diff --git a/src/rocksdb/api.cr b/src/rocksdb/api.cr
index b4279f3..e01d116 100644
--- a/src/rocksdb/api.cr
+++ b/src/rocksdb/api.cr
@@ -35,11 +35,12 @@ module RocksDB::Api
   api rocksdb_iter_seek_to_last
   api rocksdb_iter_prev
   api rocksdb_iter_next
+  api rocksdb_iter_seek
   api rocksdb_iter_key
+  api rocksdb_iter_value
   api rocksdb_iter_valid
 
 #  fun rocksdb_iter_seek(x0 : RocksdbIteratorT, k : LibC::Char*, klen : LibC::SizeT)
-#  fun rocksdb_iter_value(x0 : RocksdbIteratorT, vlen : LibC::SizeT*) : LibC::Char*
 #  fun rocksdb_iter_get_error(x0 : RocksdbIteratorT, errptr : LibC::Char**)
 
 
diff --git a/src/rocksdb/commands/iteration.cr b/src/rocksdb/commands/iteration.cr
index 0b21f70..d9f566f 100644
--- a/src/rocksdb/commands/iteration.cr
+++ b/src/rocksdb/commands/iteration.cr
@@ -1,20 +1,32 @@
 module RocksDB::Commands
   include Api
+
+  def new_iterator
+    Iterator.new(self)
+  end
   
   def each(&block)
-    iter = Iterator.new(self)
+#    iter = StringIterator.new(self)
+    iter = new_iterator
+    iter.first
+    while iter.valid?
+      yield({iter.key, iter.value})
+      iter.next
+    end
+  ensure
+    iter.try(&.close)
   end
 
   def keys(limit = Int32::MAX)
-    iter = Iterator.new(self)
-    iter.first!
+    iter = new_iterator
+    iter.first
     array = [] of String
     i = 0
     while (key = iter.key?)
       i += 1
       break if i > limit
       array << key
-      iter.next!
+      iter.next
     end
     return array
   ensure
diff --git a/src/rocksdb/db.cr b/src/rocksdb/db.cr
index bb092dd..0c06faa 100644
--- a/src/rocksdb/db.cr
+++ b/src/rocksdb/db.cr
@@ -1,8 +1,8 @@
 class RocksDB::DB
-  include Value(LibRocksDB::RocksdbT)
+  include RawMemory(LibRocksDB::RocksdbT)
   include Commands
 
-  alias RawValue = Options | ReadOptions | WriteOptions
+  alias Closable = Options | ReadOptions | WriteOptions
 
   @options       : Options
   @read_options  : ReadOptions
@@ -12,11 +12,11 @@ class RocksDB::DB
   getter! write_options
 
   def initialize(@path : String, options : Options? = nil, read_options : ReadOptions? = nil, write_options : WriteOptions? = nil)
-    @raw_values = [] of RawValue
+    @closables = [] of Closable
 
-    @options       = options       || raw_value(Options.new.set_create_if_missing(1))
-    @read_options  = read_options  || raw_value(ReadOptions.new)
-    @write_options = write_options || raw_value(WriteOptions.new)
+    @options       = options       || mark_closable(Options.new.set_create_if_missing(1))
+    @read_options  = read_options  || mark_closable(ReadOptions.new)
+    @write_options = write_options || mark_closable(WriteOptions.new)
 
     @len = Pointer(UInt64).malloc(1_u64)
     @err = Pointer(Pointer(UInt8)).malloc(1_u64)
@@ -25,8 +25,8 @@ class RocksDB::DB
   end
 
   protected def free
-    @raw_values.each(&.close)
-    @raw_values.clear
+    @closables.each(&.close)
+    @closables.clear
     rocksdb_close(@raw.not_nil!)
   end
 
@@ -34,8 +34,8 @@ class RocksDB::DB
     @path
   end
 
-  protected def raw_value(value)
-    @raw_values << value
+  protected def mark_closable(value)
+    @closables << value
     value
   end
 end
diff --git a/src/rocksdb/dsl.cr b/src/rocksdb/dsl.cr
index 5869801..123377a 100644
--- a/src/rocksdb/dsl.cr
+++ b/src/rocksdb/dsl.cr
@@ -3,7 +3,7 @@ macro option_class(klass)
   {% method  = klass.stringify.downcase %}
   class RocksDB::{{ klass.id }}
     include Api
-    include Value({{ underly.id }})
+    include RawMemory({{ underly.id }})
 
     def initialize
       @raw = rocksdb_{{ method.id }}_create
diff --git a/src/rocksdb/iterator.cr b/src/rocksdb/iterator.cr
index 26b4281..9b41efe 100644
--- a/src/rocksdb/iterator.cr
+++ b/src/rocksdb/iterator.cr
@@ -1,44 +1,63 @@
+#abstract class RocksDB::Iterator(T)
 class RocksDB::Iterator
   include Api
-  include Value(LibRocksDB::RocksdbIteratorT)
+  include RawMemory(LibRocksDB::RocksdbIteratorT)
   
-  @read_options : ReadOptions
+#  protected abstract def zero : T
+#  protected abstract def underlying(ptr, size) : T
+  protected def zero
+    ""
+  end
+
+  protected def underlying(ptr, size) : String
+    String.new(ptr, size)
+  end
 
   def initialize(@db : DB, read_options : ReadOptions? = nil)
-    @read_options = (read_options || @db.read_options).not_nil!
-    @raw = rocksdb_create_iterator(@db.raw, @read_options.raw)
+    opts = (read_options || @db.read_options).not_nil!
+    @raw = rocksdb_create_iterator(@db.raw, opts.raw)
     @len = Pointer(UInt64).malloc(1_u64)
     @opened = true
   end
 
-  def first!
+  def first
     rocksdb_iter_seek_to_first(raw)
   end
   
-  def last!
+  def last
     rocksdb_iter_seek_to_last(raw)
   end
 
-  def next!
+  def next
     rocksdb_iter_next(raw)
   end
-  
-  def prev!
+
+  def prev
     rocksdb_iter_prev(raw)
   end
-  
+
+  def seek(key)
+    rocksdb_iter_seek(raw, key, key.bytesize)
+  end
+
   def valid?
     rocksdb_iter_valid(raw) == 1
   end
 
-  def key?
-    return nil if !valid?
+  def key
     ptr = rocksdb_iter_key(raw, @len)
-    @len.value == 0 ? nil : String.new(ptr, @len.value)
+    underlying(ptr, @len.value)
   end
 
-  def key
-    key? || ""
+  def value
+    ptr = rocksdb_iter_value(raw, @len)
+    underlying(ptr, @len.value)
+  end
+
+  def key?
+    return nil if !valid?
+    ptr = rocksdb_iter_key(raw, @len)
+    @len.value == 0 ? nil : underlying(ptr, @len.value)
   end
 
   protected def free
@@ -49,9 +68,21 @@ class RocksDB::Iterator
     "iter"
   end
 
-#  fun rocksdb_iter_valid(x0 : RocksdbIteratorT) : UInt8
 #  fun rocksdb_iter_seek(x0 : RocksdbIteratorT, k : LibC::Char*, klen : LibC::SizeT)
-#  fun rocksdb_iter_value(x0 : RocksdbIteratorT, vlen : LibC::SizeT*) : LibC::Char*
 #  fun rocksdb_iter_get_error(x0 : RocksdbIteratorT, errptr : LibC::Char**)
 
 end
+
+{% if flag?(:fixed_issue3635) %}
+module RocksDB
+  class StringIterator < Iterator(String)
+    protected def zero
+      ""
+    end
+
+    protected def underlying(ptr, size) : String
+      String.new(ptr, size)
+    end
+  end
+end
+{% end %}
diff --git a/src/rocksdb/types.cr b/src/rocksdb/types.cr
index 975f8c8..57efeab 100644
--- a/src/rocksdb/types.cr
+++ b/src/rocksdb/types.cr
@@ -14,7 +14,7 @@ module RocksDB
   end
 end
 
-module RocksDB::Value(T)
+module RocksDB::RawMemory(T)
   @opened : Bool
 
   @raw : T?