Merge branch 'no-implicit-conversion' into mruby2-draftmruby2-draft

32 files changed, 174 insertions, 467 deletions

diff --git a/include/mruby.h b/include/mruby.h
index 2d30d3d27..ab5d5b167 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -716,7 +716,6 @@ MRB_API mrb_value mrb_notimplement_m(mrb_state*, mrb_value);
  * @return [mrb_value] The newly duplicated object.
  */
 MRB_API mrb_value mrb_obj_dup(mrb_state *mrb, mrb_value obj);
-MRB_API mrb_value mrb_check_to_integer(mrb_state *mrb, mrb_value val, const char *method);
 
 /**
  * Returns true if obj responds to the given method. If the method was defined for that
@@ -855,10 +854,6 @@ typedef const char *mrb_args_format;
 /**
  * Retrieve arguments from mrb_state.
  *
- * When applicable, implicit conversions (such as `to_str`, `to_ary`, `to_hash`) are
- * applied to received arguments.
- * Used inside a function of mrb_func_t type.
- *
  * @param mrb The current MRuby state.
  * @param format [mrb_args_format] is a list of format specifiers
  * @param ... The passing variadic arguments must be a pointer of retrieving type.
@@ -1188,6 +1183,7 @@ MRB_API void mrb_gc_unregister(mrb_state *mrb, mrb_value obj);
 
 MRB_API mrb_value mrb_to_int(mrb_state *mrb, mrb_value val);
 #define mrb_int(mrb, val) mrb_fixnum(mrb_to_int(mrb, val))
+MRB_API mrb_value mrb_to_str(mrb_state *mrb, mrb_value val);
 MRB_API void mrb_check_type(mrb_state *mrb, mrb_value x, enum mrb_vtype t);
 
 typedef enum call_type {
diff --git a/include/mruby/array.h b/include/mruby/array.h
index 6fffe4512..2457f68f2 100644
--- a/include/mruby/array.h
+++ b/include/mruby/array.h
@@ -199,6 +199,7 @@ MRB_API void mrb_ary_set(mrb_state *mrb, mrb_value ary, mrb_int n, mrb_value val
  * @param other The array to replace it with.
  */
 MRB_API void mrb_ary_replace(mrb_state *mrb, mrb_value self, mrb_value other);
+MRB_API mrb_value mrb_ensure_array_type(mrb_state *mrb, mrb_value self);
 MRB_API mrb_value mrb_check_array_type(mrb_state *mrb, mrb_value self);
 
 /*
diff --git a/include/mruby/string.h b/include/mruby/string.h
index 481b2fb38..fa1955f48 100644
--- a/include/mruby/string.h
+++ b/include/mruby/string.h
@@ -311,8 +311,7 @@ MRB_API mrb_value mrb_str_substr(mrb_state *mrb, mrb_value str, mrb_int beg, mrb
  * @param [mrb_value] str Ruby string.
  * @return [mrb_value] A Ruby string.
  */
-MRB_API mrb_value mrb_string_type(mrb_state *mrb, mrb_value str);
-
+MRB_API mrb_value mrb_ensure_string_type(mrb_state *mrb, mrb_value str);
 MRB_API mrb_value mrb_check_string_type(mrb_state *mrb, mrb_value str);
 MRB_API mrb_value mrb_str_new_capa(mrb_state *mrb, size_t capa);
 MRB_API mrb_value mrb_str_buf_new(mrb_state *mrb, size_t capa);
diff --git a/mrbgems/mruby-array-ext/mrblib/array.rb b/mrbgems/mruby-array-ext/mrblib/array.rb
index c0995bb99..f94d08765 100644
--- a/mrbgems/mruby-array-ext/mrblib/array.rb
+++ b/mrbgems/mruby-array-ext/mrblib/array.rb
@@ -1,31 +1,7 @@
+# coding: cp932
 class Array
   ##
   # call-seq:
-  #    Array.try_convert(obj) -> array or nil
-  #
-  # Tries to convert +obj+ into an array, using +to_ary+ method.
-  # converted array or +nil+ if +obj+ cannot be converted for any reason.
-  # This method can be used to check if an argument is an array.
-  #
-  #    Array.try_convert([1])   #=> [1]
-  #    Array.try_convert("1")   #=> nil
-  #
-  #    if tmp = Array.try_convert(arg)
-  #      # the argument is an array
-  #    elsif tmp = String.try_convert(arg)
-  #      # the argument is a string
-  #    end
-  #
-  def self.try_convert(obj)
-    if obj.respond_to?(:to_ary)
-      obj.to_ary
-    else
-      nil
-    end
-  end
-
-  ##
-  # call-seq:
   #    ary.uniq!                -> ary or nil
   #    ary.uniq! { |item| ... } -> ary or nil
   #
@@ -783,16 +759,6 @@ class Array
   end
 
   ##
-  #  call-seq:
-  #     ary.to_ary -> ary
-  #
-  #  Returns +self+.
-  #
-  def to_ary
-    self
-  end
-
-  ##
   # call-seq:
   #   ary.dig(idx, ...)                 -> object
   #
diff --git a/mrbgems/mruby-array-ext/test/array.rb b/mrbgems/mruby-array-ext/test/array.rb
index 4f54c65c3..d0b5bec6d 100644
--- a/mrbgems/mruby-array-ext/test/array.rb
+++ b/mrbgems/mruby-array-ext/test/array.rb
@@ -1,13 +1,6 @@
 ##
 # Array(Ext) Test
 
-assert("Array.try_convert") do
-  assert_nil Array.try_convert(0)
-  assert_nil Array.try_convert(nil)
-  assert_equal [], Array.try_convert([])
-  assert_equal [1,2,3], Array.try_convert([1,2,3])
-end
-
 assert("Array#assoc") do
   s1 = [ "colors", "red", "blue", "green" ]
   s2 = [ "letters", "a", "b", "c" ]
@@ -330,27 +323,11 @@ assert('Array#to_h') do
   assert_raise(ArgumentError) { [[1]].to_h }
 end
 
-assert('Array#to_h (Modified)') do
-  class A
-    def to_ary
-      $a.clear
-      nil
-    end
-  end
-  $a = [A.new]
-  assert_raise(TypeError) { $a.to_h }
-end
-
 assert("Array#index (block)") do
   assert_nil (1..10).to_a.index { |i| i % 5 == 0 and i % 7 == 0 }
   assert_equal 34, (1..100).to_a.index { |i| i % 5 == 0 and i % 7 == 0 }
 end
 
-assert("Array#to_ary") do
-  assert_equal [], [].to_ary
-  assert_equal [1,2,3], [1,2,3].to_ary
-end
-
 assert("Array#dig") do
   h = [[[1]], 0]
   assert_equal(1, h.dig(0, 0, 0))
diff --git a/mrbgems/mruby-enum-ext/mrblib/enum.rb b/mrbgems/mruby-enum-ext/mrblib/enum.rb
index a840ade3b..e33ce2c5a 100644
--- a/mrbgems/mruby-enum-ext/mrblib/enum.rb
+++ b/mrbgems/mruby-enum-ext/mrblib/enum.rb
@@ -13,10 +13,9 @@ module Enumerable
   #    a.drop(3)             #=> [4, 5, 0]
 
   def drop(n)
-    raise TypeError, "no implicit conversion of #{n.class} into Integer" unless n.respond_to?(:to_int)
+    n = n.__to_int
     raise ArgumentError, "attempt to drop negative size" if n < 0
 
-    n = n.to_int
     ary = []
     self.each {|*val| n == 0 ? ary << val.__svalue : n -= 1 }
     ary
@@ -57,8 +56,8 @@ module Enumerable
   #    a.take(3)             #=> [1, 2, 3]
 
   def take(n)
-    raise TypeError, "no implicit conversion of #{n.class} into Integer" unless n.respond_to?(:to_int)
-    i = n.to_int
+    n = n.__to_int
+    i = n.to_i
     raise ArgumentError, "attempt to take negative size" if i < 0
     ary = []
     return ary if i == 0
@@ -113,12 +112,12 @@ module Enumerable
   #     [8, 9, 10]
 
   def each_cons(n, &block)
-    raise TypeError, "no implicit conversion of #{n.class} into Integer" unless n.respond_to?(:to_int)
+    n = n.__to_int
     raise ArgumentError, "invalid size" if n <= 0
 
     return to_enum(:each_cons,n) unless block
     ary = []
-    n = n.to_int
+    n = n.to_i
     self.each do |*val|
       ary.shift if ary.size == n
       ary << val.__svalue
@@ -141,12 +140,12 @@ module Enumerable
   #     [10]
 
   def each_slice(n, &block)
-    raise TypeError, "no implicit conversion of #{n.class} into Integer" unless n.respond_to?(:to_int)
+    n = n.__to_int
     raise ArgumentError, "invalid slice size" if n <= 0
 
     return to_enum(:each_slice,n) unless block
     ary = []
-    n = n.to_int
+    n = n.to_i
     self.each do |*val|
       ary << val.__svalue
       if ary.size == n
@@ -225,9 +224,7 @@ module Enumerable
       end
       return nil
     when 1
-      n = args[0]
-      raise TypeError, "no implicit conversion of #{n.class} into Integer" unless n.respond_to?(:to_int)
-      i = n.to_int
+      i = args[0].__to_int
       raise ArgumentError, "attempt to take negative size" if i < 0
       ary = []
       return ary if i == 0
@@ -675,13 +672,7 @@ module Enumerable
     if nv.nil?
       n = -1
     else
-      unless nv.respond_to?(:to_int)
-        raise TypeError, "no implicit conversion of #{nv.class} into Integer"
-      end
-      n = nv.to_int
-      unless n.kind_of?(Integer)
-        raise TypeError, "no implicit conversion of #{nv.class} into Integer"
-      end
+      n = nv.__to_int
       return nil if n <= 0
     end
 
diff --git a/mrbgems/mruby-enumerator/mrblib/enumerator.rb b/mrbgems/mruby-enumerator/mrblib/enumerator.rb
index 7ca1d5eb6..ae692dd12 100644
--- a/mrbgems/mruby-enumerator/mrblib/enumerator.rb
+++ b/mrbgems/mruby-enumerator/mrblib/enumerator.rb
@@ -157,12 +157,10 @@ class Enumerator
   def with_index(offset=0, &block)
     return to_enum :with_index, offset unless block
 
-    offset = if offset.nil?
-      0
-    elsif offset.respond_to?(:to_int)
-      offset.to_int
+    if offset.nil?
+      offset = 0
     else
-      raise TypeError, "no implicit conversion of #{offset.class} into Integer"
+      offset = offset.__to_int
     end
 
     n = offset - 1
@@ -623,9 +621,7 @@ module Enumerable
   # use Enumerator to use infinite sequence
   def zip(*args, &block)
     args = args.map do |a|
-      if a.respond_to?(:to_ary)
-        a.to_ary.to_enum(:each)
-      elsif a.respond_to?(:each)
+      if a.respond_to?(:each)
         a.to_enum(:each)
       else
         raise TypeError, "wrong argument type #{a.class} (must respond to :each)"
diff --git a/mrbgems/mruby-enumerator/test/enumerator.rb b/mrbgems/mruby-enumerator/test/enumerator.rb
index 428ea0307..c24b70ccb 100644
--- a/mrbgems/mruby-enumerator/test/enumerator.rb
+++ b/mrbgems/mruby-enumerator/test/enumerator.rb
@@ -55,12 +55,6 @@ assert 'Enumerator#with_index' do
   assert_equal [[[1, 10], 20], [[2, 11], 21], [[3, 12], 22]], a
 end
 
-assert 'Enumerator#with_index nonnum offset' do
-  s = Object.new
-  def s.to_int; 1 end
-  assert_equal([[1,1],[2,2],[3,3]], @obj.to_enum(:foo, 1, 2, 3).with_index(s).to_a)
-end
-
 assert 'Enumerator#with_index string offset' do
   assert_raise(TypeError){ @obj.to_enum(:foo, 1, 2, 3).with_index('1').to_a }
 end
diff --git a/mrbgems/mruby-hash-ext/mrblib/hash.rb b/mrbgems/mruby-hash-ext/mrblib/hash.rb
index 61e4c890c..3c2d99836 100644
--- a/mrbgems/mruby-hash-ext/mrblib/hash.rb
+++ b/mrbgems/mruby-hash-ext/mrblib/hash.rb
@@ -27,9 +27,9 @@ class Hash
     length = object.length
     if length == 1
       o = object[0]
-      if o.respond_to?(:to_hash)
+      if Hash === o
         h = self.new
-        object[0].to_hash.each { |k, v| h[k] = v }
+        o.each { |k, v| h[k] = v }
         return h
       elsif o.respond_to?(:to_a)
         h = self.new
@@ -62,25 +62,6 @@ class Hash
 
   ##
   # call-seq:
-  #     Hash.try_convert(obj) -> hash or nil
-  #
-  # Try to convert <i>obj</i> into a hash, using to_hash method.
-  # Returns converted hash or nil if <i>obj</i> cannot be converted
-  # for any reason.
-  #
-  #     Hash.try_convert({1=>2})   # => {1=>2}
-  #     Hash.try_convert("1=>2")   # => nil
-  #
-  def self.try_convert(obj)
-    if obj.respond_to?(:to_hash)
-      obj.to_hash
-    else
-      nil
-    end
-  end
-
-  ##
-  # call-seq:
   #     hsh.merge!(other_hash)                                 -> hsh
   #     hsh.merge!(other_hash){|key, oldval, newval| block}    -> hsh
   #
@@ -101,7 +82,7 @@ class Hash
   #
 
   def merge!(other, &block)
-    raise TypeError, "can't convert argument into Hash" unless other.respond_to?(:to_hash)
+    raise TypeError, "Hash required (#{other.class} given)" unless Hash === other
     if block
       other.each_key{|k|
         self[k] = (self.has_key?(k))? block.call(k, self[k], other[k]): other[k]
@@ -329,11 +310,7 @@ class Hash
   #     h1 < h1    #=> false
   #
   def <(hash)
-    begin
-      hash = hash.to_hash
-    rescue NoMethodError
-      raise TypeError, "can't convert #{hash.class} to Hash"
-    end
+    raise TypeError, "can't convert #{hash.class} to Hash" unless Hash === hash
     size < hash.size and all? {|key, val|
       hash.key?(key) and hash[key] == val
     }
@@ -353,11 +330,7 @@ class Hash
   #     h1 <= h1   #=> true
   #
   def <=(hash)
-    begin
-      hash = hash.to_hash
-    rescue NoMethodError
-      raise TypeError, "can't convert #{hash.class} to Hash"
-    end
+    raise TypeError, "can't convert #{hash.class} to Hash" unless Hash === hash
     size <= hash.size and all? {|key, val|
       hash.key?(key) and hash[key] == val
     }
@@ -377,11 +350,7 @@ class Hash
   #     h1 > h1    #=> false
   #
   def >(hash)
-    begin
-      hash = hash.to_hash
-    rescue NoMethodError
-      raise TypeError, "can't convert #{hash.class} to Hash"
-    end
+    raise TypeError, "can't convert #{hash.class} to Hash" unless Hash === hash
     size > hash.size and hash.all? {|key, val|
       key?(key) and self[key] == val
     }
@@ -401,11 +370,7 @@ class Hash
   #     h1 >= h1   #=> true
   #
   def >=(hash)
-    begin
-      hash = hash.to_hash
-    rescue NoMethodError
-      raise TypeError, "can't convert #{hash.class} to Hash"
-    end
+    raise TypeError, "can't convert #{hash.class} to Hash" unless Hash === hash
     size >= hash.size and hash.all? {|key, val|
       key?(key) and self[key] == val
     }
diff --git a/mrbgems/mruby-hash-ext/test/hash.rb b/mrbgems/mruby-hash-ext/test/hash.rb
index 269da800d..b5d0aaaf8 100644
--- a/mrbgems/mruby-hash-ext/test/hash.rb
+++ b/mrbgems/mruby-hash-ext/test/hash.rb
@@ -45,12 +45,6 @@ assert('Hash.[] for sub class') do
   assert_equal(sub_hash_class, sub_hash.class)
 end
 
-assert('Hash.try_convert') do
-  assert_nil Hash.try_convert(nil)
-  assert_nil Hash.try_convert("{1=>2}")
-  assert_equal({1=>2}, Hash.try_convert({1=>2}))
-end
-
 assert('Hash#merge!') do
   a = { 'abc_key' => 'abc_value', 'cba_key' => 'cba_value' }
   b = { 'cba_key' => 'XXX',  'xyz_key' => 'xyz_value' }
diff --git a/mrbgems/mruby-io/src/file.c b/mrbgems/mruby-io/src/file.c
index e65741061..c00663481 100644
--- a/mrbgems/mruby-io/src/file.c
+++ b/mrbgems/mruby-io/src/file.c
@@ -115,7 +115,7 @@ mrb_file_s_unlink(mrb_state *mrb, mrb_value obj)
   mrb_get_args(mrb, "*", &argv, &argc);
   for (i = 0; i < argc; i++) {
     const char *utf8_path;
-    pathv = mrb_convert_type(mrb, argv[i], MRB_TT_STRING, "String", "to_str");
+    pathv = mrb_ensure_string_type(mrb, argv[i]);
     utf8_path = mrb_string_value_cstr(mrb, &pathv);
     path = mrb_locale_from_utf8(utf8_path, -1);
     if (UNLINK(path) < 0) {
diff --git a/mrbgems/mruby-kernel-ext/src/kernel.c b/mrbgems/mruby-kernel-ext/src/kernel.c
index 32d86376a..99affbfa4 100644
--- a/mrbgems/mruby-kernel-ext/src/kernel.c
+++ b/mrbgems/mruby-kernel-ext/src/kernel.c
@@ -93,9 +93,8 @@ mrb_f_method(mrb_state *mrb, mrb_value self)
  *  (<code>0</code>, <code>0b</code>, and <code>0x</code>) are honored.
  *  In any case, strings should be strictly conformed to numeric
  *  representation. This behavior is different from that of
- *  <code>String#to_i</code>.  Non string values will be converted using
- *  <code>to_int</code>, and <code>to_i</code>. Passing <code>nil</code>
- *  raises a TypeError.
+ *  <code>String#to_i</code>.  Non string values will be treated as integers.
+ *  Passing <code>nil</code> raises a TypeError.
  *
  *     Integer(123.999)    #=> 123
  *     Integer("0x1a")     #=> 26
@@ -142,8 +141,7 @@ mrb_f_float(mrb_state *mrb, mrb_value self)
  *     String(arg)   -> string
  *
  *  Returns <i>arg</i> as an <code>String</code>.
- *
- *  First tries to call its <code>to_str</code> method, then its to_s method.
+ *  converted using <code>to_s</code> method.
  *
  *     String(self)        #=> "main"
  *     String(self.class)  #=> "Object"
@@ -155,10 +153,7 @@ mrb_f_string(mrb_state *mrb, mrb_value self)
   mrb_value arg, tmp;
 
   mrb_get_args(mrb, "o", &arg);
-  tmp = mrb_check_convert_type(mrb, arg, MRB_TT_STRING, "String", "to_str");
-  if (mrb_nil_p(tmp)) {
-    tmp = mrb_check_convert_type(mrb, arg, MRB_TT_STRING, "String", "to_s");
-  }
+  tmp = mrb_convert_type(mrb, arg, MRB_TT_STRING, "String", "to_s");
   return tmp;
 }
 
@@ -166,9 +161,7 @@ mrb_f_string(mrb_state *mrb, mrb_value self)
  *  call-seq:
  *     Array(arg)    -> array
  *
- *  Returns +arg+ as an Array.
- *
- *  First tries to call Array#to_ary on +arg+, then Array#to_a.
+ *  Returns +arg+ as an Array using to_a method.
  *
  *     Array(1..5)   #=> [1, 2, 3, 4, 5]
  *
@@ -179,10 +172,7 @@ mrb_f_array(mrb_state *mrb, mrb_value self)
   mrb_value arg, tmp;
 
   mrb_get_args(mrb, "o", &arg);
-  tmp = mrb_check_convert_type(mrb, arg, MRB_TT_ARRAY, "Array", "to_ary");
-  if (mrb_nil_p(tmp)) {
-    tmp = mrb_check_convert_type(mrb, arg, MRB_TT_ARRAY, "Array", "to_a");
-  }
+  tmp = mrb_check_convert_type(mrb, arg, MRB_TT_ARRAY, "Array", "to_a");
   if (mrb_nil_p(tmp)) {
     return mrb_ary_new_from_values(mrb, 1, &arg);
   }
@@ -194,9 +184,9 @@ mrb_f_array(mrb_state *mrb, mrb_value self)
  *  call-seq:
  *     Hash(arg)    -> hash
  *
- *  Converts <i>arg</i> to a <code>Hash</code> by calling
- *  <i>arg</i><code>.to_hash</code>. Returns an empty <code>Hash</code> when
- *  <i>arg</i> is <tt>nil</tt> or <tt>[]</tt>.
+ *  Returns a <code>Hash</code> if <i>arg</i> is a <code>Hash</code>.
+ *  Returns an empty <code>Hash</code> when <i>arg</i> is <tt>nil</tt>
+ *  or <tt>[]</tt>.
  *
  *      Hash([])          #=> {}
  *      Hash(nil)         #=> {}
@@ -207,21 +197,13 @@ mrb_f_array(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_f_hash(mrb_state *mrb, mrb_value self)
 {
-  mrb_value arg, tmp;
+  mrb_value arg;
 
   mrb_get_args(mrb, "o", &arg);
-  if (mrb_nil_p(arg)) {
+  if (mrb_nil_p(arg) || (mrb_array_p(arg) && RARRAY_LEN(arg) == 0)) {
     return mrb_hash_new(mrb);
   }
-  tmp = mrb_check_convert_type(mrb, arg, MRB_TT_HASH, "Hash", "to_hash");
-  if (mrb_nil_p(tmp)) {
-    if (mrb_array_p(arg) && RARRAY_LEN(arg) == 0) {
-      return mrb_hash_new(mrb);
-    }
-    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S into Hash",
-      mrb_str_new_cstr(mrb, mrb_obj_classname(mrb, arg)));
-  }
-  return tmp;
+  return mrb_ensure_hash_type(mrb, arg);
 }
 
 /*
diff --git a/mrbgems/mruby-numeric-ext/src/numeric_ext.c b/mrbgems/mruby-numeric-ext/src/numeric_ext.c
index 1d6a07769..cd8bbf187 100644
--- a/mrbgems/mruby-numeric-ext/src/numeric_ext.c
+++ b/mrbgems/mruby-numeric-ext/src/numeric_ext.c
@@ -2,13 +2,10 @@
 #include <mruby.h>
 
 static inline mrb_int
-to_int(mrb_value x)
+to_int(mrb_state *mrb, mrb_value x)
 {
-  double f;
-
-  if (mrb_fixnum_p(x)) return mrb_fixnum(x);
-  f = mrb_float(x);
-  return (mrb_int)f;
+  x = mrb_to_int(mrb, x);
+  return mrb_fixnum(x);
 }
 
 /*
@@ -28,7 +25,7 @@ mrb_int_chr(mrb_state *mrb, mrb_value x)
   mrb_int chr;
   char c;
 
-  chr = to_int(x);
+  chr = to_int(mrb, x);
   if (chr >= (1 << CHAR_BIT)) {
     mrb_raisef(mrb, E_RANGE_ERROR, "%S out of char range", x);
   }
@@ -48,8 +45,8 @@ mrb_int_allbits(mrb_state *mrb, mrb_value self)
 {
   mrb_int n, m;
 
-  n = to_int(self);
   mrb_get_args(mrb, "i", &m);
+  n = to_int(mrb, self);
   return mrb_bool_value((n & m) == m);
 }
 
@@ -64,8 +61,8 @@ mrb_int_anybits(mrb_state *mrb, mrb_value self)
 {
   mrb_int n, m;
 
-  n = to_int(self);
   mrb_get_args(mrb, "i", &m);
+  n = to_int(mrb, self);
   return mrb_bool_value((n & m) != 0);
 }
 
@@ -80,8 +77,8 @@ mrb_int_nobits(mrb_state *mrb, mrb_value self)
 {
   mrb_int n, m;
 
-  n = to_int(self);
   mrb_get_args(mrb, "i", &m);
+  n = to_int(mrb, self);
   return mrb_bool_value((n & m) == 0);
 }
 
diff --git a/mrbgems/mruby-pack/src/pack.c b/mrbgems/mruby-pack/src/pack.c
index f970d9339..0fa8c90bd 100644
--- a/mrbgems/mruby-pack/src/pack.c
+++ b/mrbgems/mruby-pack/src/pack.c
@@ -1124,14 +1124,16 @@ mrb_pack_pack(mrb_state *mrb, mrb_value ary)
       o = mrb_ary_ref(mrb, ary, aidx);
       if (type == PACK_TYPE_INTEGER) {
         o = mrb_to_int(mrb, o);
+      }
 #ifndef MRB_WITHOUT_FLOAT
-      } else if (type == PACK_TYPE_FLOAT) {
+      else if (type == PACK_TYPE_FLOAT) {
         if (!mrb_float_p(o)) {
           mrb_float f = mrb_to_flo(mrb, o);
           o = mrb_float_value(mrb, f);
         }
+      }
 #endif
-      } else if (type == PACK_TYPE_STRING) {
+      else if (type == PACK_TYPE_STRING) {
         if (!mrb_string_p(o)) {
           mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S into String", mrb_class_path(mrb, mrb_obj_class(mrb, o)));
         }
diff --git a/mrbgems/mruby-random/src/random.c b/mrbgems/mruby-random/src/random.c
index 5b926a228..68209840a 100644
--- a/mrbgems/mruby-random/src/random.c
+++ b/mrbgems/mruby-random/src/random.c
@@ -79,12 +79,12 @@ get_opt(mrb_state* mrb)
   mrb_get_args(mrb, "|o", &arg);
 
   if (!mrb_nil_p(arg)) {
-    arg = mrb_check_convert_type(mrb, arg, MRB_TT_FIXNUM, "Fixnum", "to_int");
-    if (mrb_nil_p(arg)) {
-      mrb_raise(mrb, E_ARGUMENT_ERROR, "invalid argument type");
-    }
-    if (mrb_fixnum(arg) < 0) {
-      arg = mrb_fixnum_value(0 - mrb_fixnum(arg));
+    mrb_int i;
+
+    arg = mrb_to_int(mrb, arg);
+    i = mrb_fixnum(arg);
+    if (i < 0) {
+      arg = mrb_fixnum_value(0 - i);
     }
   }
   return arg;
diff --git a/mrbgems/mruby-random/test/random.rb b/mrbgems/mruby-random/test/random.rb
index 1c59be3a6..1653ae4a6 100644
--- a/mrbgems/mruby-random/test/random.rb
+++ b/mrbgems/mruby-random/test/random.rb
@@ -74,15 +74,3 @@ assert('Array#shuffle!(random)') do
 
   ary1 != [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] and 10.times { |x| ary1.include? x } and ary1 == ary2
 end
-
-assert('Array#sample checks input length after reading arguments') do
-  $ary = [1, 2, 3]
-  class ArrayChange
-    def to_i
-      $ary << 4
-      4
-    end
-  end
-
-  assert_equal [1, 2, 3, 4], $ary.sample(ArrayChange.new).sort
-end
diff --git a/mrbgems/mruby-range-ext/mrblib/range.rb b/mrbgems/mruby-range-ext/mrblib/range.rb
index e5d1fb079..de7925ba7 100644
--- a/mrbgems/mruby-range-ext/mrblib/range.rb
+++ b/mrbgems/mruby-range-ext/mrblib/range.rb
@@ -15,10 +15,7 @@ class Range
 
     raise ArgumentError, "wrong number of arguments (given #{args.length}, expected 1)" unless args.length == 1
     nv = args[0]
-    raise TypeError, "no implicit conversion from nil to integer" if nv.nil?
-    raise TypeError, "no implicit conversion of #{nv.class} into Integer" unless nv.respond_to?(:to_int)
-    n = nv.to_int
-    raise TypeError, "no implicit conversion of #{nv.class} into Integer" unless n.kind_of?(Integer)
+    n = nv.__to_int
     raise ArgumentError, "negative array size (or size too big)" unless 0 <= n
     ary = []
     each do |i|
diff --git a/mrbgems/mruby-sprintf/src/sprintf.c b/mrbgems/mruby-sprintf/src/sprintf.c
index 15d7b5464..5a4a7899e 100644
--- a/mrbgems/mruby-sprintf/src/sprintf.c
+++ b/mrbgems/mruby-sprintf/src/sprintf.c
@@ -233,7 +233,7 @@ get_hash(mrb_state *mrb, mrb_value *hash, mrb_int argc, const mrb_value *argv)
   if (argc != 2) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "one hash required");
   }
-  tmp = mrb_check_convert_type(mrb, argv[1], MRB_TT_HASH, "Hash", "to_hash");
+  tmp = mrb_check_hash_type(mrb, argv[1]);
   if (mrb_nil_p(tmp)) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "one hash required");
   }
diff --git a/mrbgems/mruby-string-ext/mrblib/string.rb b/mrbgems/mruby-string-ext/mrblib/string.rb
index 27ca30610..2a323c858 100644
--- a/mrbgems/mruby-string-ext/mrblib/string.rb
+++ b/mrbgems/mruby-string-ext/mrblib/string.rb
@@ -1,25 +1,6 @@
 class String
 
   ##
-  #  call-seq:
-  #     String.try_convert(obj) -> string or nil
-  #
-  # Try to convert <i>obj</i> into a String, using to_str method.
-  # Returns converted string or nil if <i>obj</i> cannot be converted
-  # for any reason.
-  #
-  #     String.try_convert("str")     #=> "str"
-  #     String.try_convert(/re/)      #=> nil
-  #
-  def self.try_convert(obj)
-    if obj.respond_to?(:to_str)
-      obj.to_str
-    else
-      nil
-    end
-  end
-
-  ##
   # call-seq:
   #    string.clear    ->  string
   #
@@ -142,7 +123,7 @@ class String
   #    "abcdef".casecmp("ABCDEF")    #=> 0
   #
   def casecmp(str)
-    self.downcase <=> str.to_str.downcase
+    self.downcase <=> str.__to_str.downcase
   rescue NoMethodError
     nil
   end
diff --git a/mrbgems/mruby-string-ext/src/string.c b/mrbgems/mruby-string-ext/src/string.c
index 142d449f4..7f48efe48 100644
--- a/mrbgems/mruby-string-ext/src/string.c
+++ b/mrbgems/mruby-string-ext/src/string.c
@@ -163,7 +163,7 @@ mrb_str_concat_m(mrb_state *mrb, mrb_value self)
   if (mrb_fixnum_p(str))
     str = mrb_fixnum_chr(mrb, str);
   else
-    str = mrb_string_type(mrb, str);
+    str = mrb_ensure_string_type(mrb, str);
   mrb_str_concat(mrb, self, str);
   return self;
 }
@@ -191,7 +191,7 @@ mrb_str_start_with(mrb_state *mrb, mrb_value self)
   for (i = 0; i < argc; i++) {
     size_t len_l, len_r;
     int ai = mrb_gc_arena_save(mrb);
-    sub = mrb_string_type(mrb, argv[i]);
+    sub = mrb_ensure_string_type(mrb, argv[i]);
     mrb_gc_arena_restore(mrb, ai);
     len_l = RSTRING_LEN(self);
     len_r = RSTRING_LEN(sub);
@@ -220,7 +220,7 @@ mrb_str_end_with(mrb_state *mrb, mrb_value self)
   for (i = 0; i < argc; i++) {
     size_t len_l, len_r;
     int ai = mrb_gc_arena_save(mrb);
-    sub = mrb_string_type(mrb, argv[i]);
+    sub = mrb_ensure_string_type(mrb, argv[i]);
     mrb_gc_arena_restore(mrb, ai);
     len_l = RSTRING_LEN(self);
     len_r = RSTRING_LEN(sub);
diff --git a/mrbgems/mruby-string-ext/test/string.rb b/mrbgems/mruby-string-ext/test/string.rb
index b6146fb90..b44e8181a 100644
--- a/mrbgems/mruby-string-ext/test/string.rb
+++ b/mrbgems/mruby-string-ext/test/string.rb
@@ -4,13 +4,6 @@
 
 UTF8STRING = ("\343\201\202".size == 1)
 
-assert('String.try_convert') do
-  assert_nil String.try_convert(nil)
-  assert_nil String.try_convert(:foo)
-  assert_equal "", String.try_convert("")
-  assert_equal "1,2,3", String.try_convert("1,2,3")
-end
-
 assert('String#getbyte') do
   str1 = "hello"
   bytes1 = [104, 101, 108, 108, 111]
@@ -31,18 +24,6 @@ assert('String#setbyte') do
   assert_equal("Hello", str1)
 end
 
-assert("String#setbyte raises IndexError if arg conversion resizes String") do
-  $s = "01234\n"
-  class Tmp
-      def to_i
-          $s.chomp! ''
-          95
-      end
-  end
-  tmp = Tmp.new
-  assert_raise(IndexError) { $s.setbyte(5, tmp) }
-end
-
 assert('String#byteslice') do
   str1 = "hello"
   assert_equal("e", str1.byteslice(1))
@@ -126,12 +107,6 @@ assert('String#concat') do
   assert_equal "Hello World!", "Hello " << "World" << 33
   assert_equal "Hello World!", "Hello ".concat("World").concat(33)
 
-  o = Object.new
-  def o.to_str
-    "to_str"
-  end
-  assert_equal "hi to_str", "hi " << o
-
   assert_raise(TypeError) { "".concat(Object.new) }
 end
 
@@ -140,11 +115,6 @@ assert('String#casecmp') do
   assert_equal 0, "aBcDeF".casecmp("abcdef")
   assert_equal(-1, "abcdef".casecmp("abcdefg"))
   assert_equal 0, "abcdef".casecmp("ABCDEF")
-  o = Object.new
-  def o.to_str
-    "ABCDEF"
-  end
-  assert_equal 0, "abcdef".casecmp(o)
 end
 
 assert('String#start_with?') do
diff --git a/mrblib/array.rb b/mrblib/array.rb
index 13c5d646c..16c602ba0 100644
--- a/mrblib/array.rb
+++ b/mrblib/array.rb
@@ -66,7 +66,7 @@ class Array
   #
   # ISO 15.2.12.5.15
   def initialize(size=0, obj=nil, &block)
-    raise TypeError, "expected Integer for 1st argument" unless size.kind_of? Integral
+    size = size.__to_int
     raise ArgumentError, "negative array size" if size < 0
 
     self.clear
diff --git a/mrblib/hash.rb b/mrblib/hash.rb
index 96029a230..1cd039c45 100644
--- a/mrblib/hash.rb
+++ b/mrblib/hash.rb
@@ -12,9 +12,7 @@ class Hash
   # ISO 15.2.13.4.1
   def ==(hash)
     return true if self.equal?(hash)
-    begin
-      hash = hash.to_hash
-    rescue NoMethodError
+    unless Hash === hash
       return false
     end
     return false if self.size != hash.size
@@ -32,9 +30,7 @@ class Hash
   # ISO 15.2.13.4.32 (x)
   def eql?(hash)
     return true if self.equal?(hash)
-    begin
-      hash = hash.to_hash
-    rescue NoMethodError
+    unless Hash === hash
       return false
     end
     return false if self.size != hash.size
@@ -154,9 +150,8 @@ class Hash
   #
   # ISO 15.2.13.4.23
   def replace(hash)
-    raise TypeError, "can't convert argument into Hash" unless hash.respond_to?(:to_hash)
+    raise TypeError, "Hash required (#{hash.class} given)" unless Hash === hash
     self.clear
-    hash = hash.to_hash
     hash.each_key{|k|
       self[k] = hash[k]
     }
@@ -179,8 +174,7 @@ class Hash
   #
   # ISO 15.2.13.4.22
   def merge(other, &block)
-    raise TypeError, "can't convert argument into Hash" unless other.respond_to?(:to_hash)
-    other = other.to_hash
+    raise TypeError, "Hash required (#{other.class} given)" unless Hash === other
     h = self.dup
     if block
       other.each_key{|k|
diff --git a/mrblib/string.rb b/mrblib/string.rb
index 07b80b340..397603e9d 100644
--- a/mrblib/string.rb
+++ b/mrblib/string.rb
@@ -12,7 +12,7 @@ class String
   def each_line(rs = "\n", &block)
     return to_enum(:each_line, rs, &block) unless block
     return block.call(self) if rs.nil?
-    rs = rs.to_str
+    rs = rs.__to_str
     offset = 0
     rs_len = rs.length
     this = dup
@@ -67,7 +67,7 @@ class String
       block = nil
     end
     if !replace.nil? || !block
-      replace = replace.to_str
+      replace = replace.__to_str
     end
     offset = 0
     result = []
@@ -129,12 +129,12 @@ class String
     end
 
     pattern, replace = *args
-    pattern = pattern.to_str
+    pattern = pattern.__to_str
     if args.length == 2 && block
       block = nil
     end
     unless block
-      replace = replace.to_str
+      replace = replace.__to_str
     end
     result = []
     this = dup
@@ -245,14 +245,13 @@ class String
   ##
   # ISO 15.2.10.5.3
   def =~(re)
-    raise TypeError, "type mismatch: String given" if re.respond_to? :to_str
     re =~ self
   end
 
   ##
   # ISO 15.2.10.5.27
   def match(re, &block)
-    if re.respond_to? :to_str
+    if String === re
       if Object.const_defined?(:Regexp)
         r = Regexp.new(re)
         r.match(self, &block)
diff --git a/src/array.c b/src/array.c
index 0b039a6ec..32ee3434e 100644
--- a/src/array.c
+++ b/src/array.c
@@ -1058,7 +1058,7 @@ mrb_ary_rindex_m(mrb_state *mrb, mrb_value self)
 MRB_API mrb_value
 mrb_ary_splat(mrb_state *mrb, mrb_value v)
 {
-  mrb_value a, recv_class;
+  mrb_value a;
 
   if (mrb_array_p(v)) {
     return v;
@@ -1069,22 +1069,11 @@ mrb_ary_splat(mrb_state *mrb, mrb_value v)
   }
 
   a = mrb_funcall(mrb, v, "to_a", 0);
-  if (mrb_array_p(a)) {
-    return a;
-  }
-  else if (mrb_nil_p(a)) {
+  if (mrb_nil_p(a)) {
     return mrb_ary_new_from_values(mrb, 1, &v);
   }
-  else {
-    recv_class = mrb_obj_value(mrb_obj_class(mrb, v));
-    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S to Array (%S#to_a gives %S)",
-      recv_class,
-      recv_class,
-      mrb_obj_value(mrb_obj_class(mrb, a))
-    );
-    /* not reached */
-    return mrb_undef_value();
-  }
+  mrb_ensure_array_type(mrb, a);
+  return a;
 }
 
 static mrb_value
@@ -1122,12 +1111,6 @@ mrb_ary_empty_p(mrb_state *mrb, mrb_value self)
 }
 
 MRB_API mrb_value
-mrb_check_array_type(mrb_state *mrb, mrb_value ary)
-{
-  return mrb_check_convert_type(mrb, ary, MRB_TT_ARRAY, "Array", "to_ary");
-}
-
-MRB_API mrb_value
 mrb_ary_entry(mrb_value ary, mrb_int offset)
 {
   if (offset < 0) {
@@ -1180,7 +1163,7 @@ join_ary(mrb_state *mrb, mrb_value ary, mrb_value sep, mrb_value list)
           val = tmp;
           goto str_join;
         }
-        tmp = mrb_check_convert_type(mrb, val, MRB_TT_ARRAY, "Array", "to_ary");
+        tmp = mrb_check_array_type(mrb, val);
         if (!mrb_nil_p(tmp)) {
           val = tmp;
           goto ary_join;
diff --git a/src/class.c b/src/class.c
index 76c699881..b5a492d8f 100644
--- a/src/class.c
+++ b/src/class.c
@@ -492,34 +492,31 @@ mrb_notimplement_m(mrb_state *mrb, mrb_value self)
   return mrb_nil_value();
 }
 
-static mrb_value
-check_type(mrb_state *mrb, mrb_value val, enum mrb_vtype t, const char *c, const char *m)
-{
-  mrb_value tmp;
-
-  tmp = mrb_check_convert_type(mrb, val, t, c, m);
-  if (mrb_nil_p(tmp)) {
-    mrb_raisef(mrb, E_TYPE_ERROR, "expected %S", mrb_str_new_cstr(mrb, c));
-  }
-  return tmp;
-}
+#define CHECK_TYPE(mrb, val, t, c) do { \
+  if (mrb_type(val) != (t)) {\
+    mrb_raisef(mrb, E_TYPE_ERROR, "expected %S", mrb_str_new_lit(mrb, c));\
+  }\
+} while (0)
 
 static mrb_value
 to_str(mrb_state *mrb, mrb_value val)
 {
-  return check_type(mrb, val, MRB_TT_STRING, "String", "to_str");
+  CHECK_TYPE(mrb, val, MRB_TT_STRING, "String");
+  return val;
 }
 
 static mrb_value
 to_ary(mrb_state *mrb, mrb_value val)
 {
-  return check_type(mrb, val, MRB_TT_ARRAY, "Array", "to_ary");
+  CHECK_TYPE(mrb, val, MRB_TT_ARRAY, "Array");
+  return val;
 }
 
 static mrb_value
 to_hash(mrb_state *mrb, mrb_value val)
 {
-  return check_type(mrb, val, MRB_TT_HASH, "Hash", "to_hash");
+  CHECK_TYPE(mrb, val, MRB_TT_HASH, "Hash");
+  return val;
 }
 
 #define to_sym(mrb, ss) mrb_obj_to_sym(mrb, ss)
@@ -1971,7 +1968,7 @@ mrb_mod_const_get(mrb_state *mrb, mrb_value mod)
   }
 
   /* const get with class path string */
-  path = mrb_string_type(mrb, path);
+  path = mrb_ensure_string_type(mrb, path);
   ptr = RSTRING_PTR(path);
   len = RSTRING_LEN(path);
   off = 0;
diff --git a/src/hash.c b/src/hash.c
index f6b61f4e1..734f6d9bd 100644
--- a/src/hash.c
+++ b/src/hash.c
@@ -320,18 +320,6 @@ mrb_hash_set(mrb_state *mrb, mrb_value hash, mrb_value key, mrb_value val)
   return;
 }
 
-MRB_API mrb_value
-mrb_ensure_hash_type(mrb_state *mrb, mrb_value hash)
-{
-  return mrb_convert_type(mrb, hash, MRB_TT_HASH, "Hash", "to_hash");
-}
-
-MRB_API mrb_value
-mrb_check_hash_type(mrb_state *mrb, mrb_value hash)
-{
-  return mrb_check_convert_type(mrb, hash, MRB_TT_HASH, "Hash", "to_hash");
-}
-
 MRB_API khash_t(ht)*
 mrb_hash_tbl(mrb_state *mrb, mrb_value hash)
 {
@@ -787,20 +775,6 @@ mrb_hash_empty_m(mrb_state *mrb, mrb_value self)
   return mrb_false_value();
 }
 
-/* 15.2.13.4.29 (x)*/
-/*
- * call-seq:
- *    hsh.to_hash   => hsh
- *
- * Returns +self+.
- */
-
-static mrb_value
-mrb_hash_to_hash(mrb_state *mrb, mrb_value hash)
-{
-  return hash;
-}
-
 /* 15.2.13.4.19 */
 /*
  *  call-seq:
@@ -1022,6 +996,4 @@ mrb_init_hash(mrb_state *mrb)
   mrb_define_method(mrb, h, "store",           mrb_hash_aset,        MRB_ARGS_REQ(2)); /* 15.2.13.4.26 */
   mrb_define_method(mrb, h, "value?",          mrb_hash_has_value,   MRB_ARGS_REQ(1)); /* 15.2.13.4.27 */
   mrb_define_method(mrb, h, "values",          mrb_hash_values,      MRB_ARGS_NONE()); /* 15.2.13.4.28 */
-
-  mrb_define_method(mrb, h, "to_hash",         mrb_hash_to_hash,     MRB_ARGS_NONE()); /* 15.2.13.4.29 (x)*/
 }
diff --git a/src/kernel.c b/src/kernel.c
index db681d510..ce9cd1d44 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -746,6 +746,7 @@ basic_obj_respond_to(mrb_state *mrb, mrb_value obj, mrb_sym id, int pub)
 {
   return mrb_respond_to(mrb, obj, id);
 }
+
 /* 15.3.1.3.43 */
 /*
  *  call-seq:
@@ -765,45 +766,16 @@ basic_obj_respond_to(mrb_state *mrb, mrb_value obj, mrb_sym id, int pub)
 static mrb_value
 obj_respond_to(mrb_state *mrb, mrb_value self)
 {
-  mrb_value mid;
   mrb_sym id, rtm_id;
-  mrb_bool priv = FALSE, respond_to_p = TRUE;
-
-  mrb_get_args(mrb, "o|b", &mid, &priv);
-
-  if (mrb_symbol_p(mid)) {
-    id = mrb_symbol(mid);
-  }
-  else {
-    mrb_value tmp;
-    if (mrb_string_p(mid)) {
-      tmp = mrb_check_intern_str(mrb, mid);
-    }
-    else {
-      tmp = mrb_check_string_type(mrb, mid);
-      if (mrb_nil_p(tmp)) {
-        tmp = mrb_inspect(mrb, mid);
-        mrb_raisef(mrb, E_TYPE_ERROR, "%S is not a symbol", tmp);
-      }
-      tmp = mrb_check_intern_str(mrb, tmp);
-    }
-    if (mrb_nil_p(tmp)) {
-      respond_to_p = FALSE;
-    }
-    else {
-      id = mrb_symbol(tmp);
-    }
-  }
-
-  if (respond_to_p) {
-    respond_to_p = basic_obj_respond_to(mrb, self, id, !priv);
-  }
+  mrb_bool priv = FALSE, respond_to_p;
 
+  mrb_get_args(mrb, "n|b", &id, &priv);
+  respond_to_p = basic_obj_respond_to(mrb, self, id, !priv);
   if (!respond_to_p) {
     rtm_id = mrb_intern_lit(mrb, "respond_to_missing?");
     if (basic_obj_respond_to(mrb, self, rtm_id, !priv)) {
       mrb_value args[2], v;
-      args[0] = mid;
+      args[0] = mrb_symbol_value(id);
       args[1] = mrb_bool_value(priv);
       v = mrb_funcall_argv(mrb, self, rtm_id, 2, args);
       return mrb_bool_value(mrb_bool(v));
@@ -830,6 +802,7 @@ mrb_obj_ceqq(mrb_state *mrb, mrb_value self)
 }
 
 mrb_value mrb_obj_equal_m(mrb_state *mrb, mrb_value);
+
 void
 mrb_init_kernel(mrb_state *mrb)
 {
@@ -871,6 +844,8 @@ mrb_init_kernel(mrb_state *mrb)
   mrb_define_method(mrb, krn, "respond_to?",                obj_respond_to,                  MRB_ARGS_ANY());     /* 15.3.1.3.43 */
   mrb_define_method(mrb, krn, "to_s",                       mrb_any_to_s,                    MRB_ARGS_NONE());    /* 15.3.1.3.46 */
   mrb_define_method(mrb, krn, "__case_eqq",                 mrb_obj_ceqq,                    MRB_ARGS_REQ(1));    /* internal */
+  mrb_define_method(mrb, krn, "__to_int",                   mrb_to_int,                      MRB_ARGS_NONE()); /* internal */
+  mrb_define_method(mrb, krn, "__to_str",                   mrb_to_str,                      MRB_ARGS_NONE()); /* internal */
 
   mrb_define_method(mrb, krn, "class_defined?",             mrb_krn_class_defined,           MRB_ARGS_REQ(1));
 
diff --git a/src/numeric.c b/src/numeric.c
index f7f0318e8..3624831cc 100644
--- a/src/numeric.c
+++ b/src/numeric.c
@@ -674,7 +674,6 @@ flo_round(mrb_state *mrb, mrb_value num)
 /*
  *  call-seq:
  *     flt.to_i      ->  integer
- *     flt.to_int    ->  integer
  *     flt.truncate  ->  integer
  *
  *  Returns <i>flt</i> truncated to an <code>Integer</code>.
@@ -714,7 +713,6 @@ flo_nan_p(mrb_state *mrb, mrb_value num)
 /*
  *  call-seq:
  *     int.to_i      ->  integer
- *     int.to_int    ->  integer
  *
  *  As <i>int</i> is already an <code>Integer</code>, all these
  *  methods simply return the receiver.
@@ -1513,7 +1511,6 @@ mrb_init_numeric(mrb_state *mrb)
   MRB_SET_INSTANCE_TT(integer, MRB_TT_FIXNUM);
   mrb_undef_class_method(mrb, integer, "new");
   mrb_define_method(mrb, integer, "to_i",     int_to_i,        MRB_ARGS_NONE()); /* 15.2.8.3.24 */
-  mrb_define_method(mrb, integer, "to_int",   int_to_i,        MRB_ARGS_NONE());
 #ifndef MRB_WITHOUT_FLOAT
   mrb_define_method(mrb, integer, "ceil",     int_to_i,        MRB_ARGS_REQ(1)); /* 15.2.8.3.8 (x) */
   mrb_define_method(mrb, integer, "floor",    int_to_i,        MRB_ARGS_REQ(1)); /* 15.2.8.3.10 (x) */
@@ -1565,7 +1562,6 @@ mrb_init_numeric(mrb_state *mrb)
   mrb_define_method(mrb, fl,      "round",     flo_round,      MRB_ARGS_OPT(1)); /* 15.2.9.3.12 */
   mrb_define_method(mrb, fl,      "to_f",      flo_to_f,       MRB_ARGS_NONE()); /* 15.2.9.3.13 */
   mrb_define_method(mrb, fl,      "to_i",      flo_truncate,   MRB_ARGS_NONE()); /* 15.2.9.3.14 */
-  mrb_define_method(mrb, fl,      "to_int",    flo_truncate,   MRB_ARGS_NONE());
   mrb_define_method(mrb, fl,      "truncate",  flo_truncate,   MRB_ARGS_NONE()); /* 15.2.9.3.15 */
   mrb_define_method(mrb, fl,      "divmod",    flo_divmod,     MRB_ARGS_REQ(1));
   mrb_define_method(mrb, fl,      "eql?",      flo_eql,        MRB_ARGS_REQ(1)); /* 15.2.8.3.16 */
diff --git a/src/object.c b/src/object.c
index 8724c5416..66dfa0f97 100644
--- a/src/object.c
+++ b/src/object.c
@@ -323,19 +323,6 @@ convert_type(mrb_state *mrb, mrb_value val, const char *tname, const char *metho
 }
 
 MRB_API mrb_value
-mrb_check_to_integer(mrb_state *mrb, mrb_value val, const char *method)
-{
-  mrb_value v;
-
-  if (mrb_fixnum_p(val)) return val;
-  v = convert_type(mrb, val, "Integer", method, FALSE);
-  if (mrb_nil_p(v) || !mrb_fixnum_p(v)) {
-    return mrb_nil_value();
-  }
-  return v;
-}
-
-MRB_API mrb_value
 mrb_convert_type(mrb_state *mrb, mrb_value val, enum mrb_vtype type, const char *tname, const char *method)
 {
   mrb_value v;
@@ -505,25 +492,22 @@ mrb_obj_is_kind_of(mrb_state *mrb, mrb_value obj, struct RClass *c)
   return FALSE;
 }
 
-static mrb_value
-mrb_to_integer(mrb_state *mrb, mrb_value val, const char *method)
-{
-  mrb_value v;
-
-  if (mrb_fixnum_p(val)) return val;
-  v = convert_type(mrb, val, "Integer", method, TRUE);
-  if (!mrb_obj_is_kind_of(mrb, v, mrb->fixnum_class)) {
-    mrb_value type = inspect_type(mrb, val);
-    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S to Integer (%S#%S gives %S)",
-               type, type, mrb_str_new_cstr(mrb, method), inspect_type(mrb, v));
-  }
-  return v;
-}
-
 MRB_API mrb_value
 mrb_to_int(mrb_state *mrb, mrb_value val)
 {
-  return mrb_to_integer(mrb, val, "to_int");
+
+  if (!mrb_fixnum_p(val)) {
+    mrb_value type;
+
+#ifndef MRB_WITHOUT_FLOAT
+    if (mrb_float_p(val)) {
+      return mrb_flo_to_fixnum(mrb, val);
+    }
+#endif
+    type = inspect_type(mrb, val);
+    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S to Integer", type);
+  }
+  return val;
 }
 
 MRB_API mrb_value
@@ -533,18 +517,12 @@ mrb_convert_to_integer(mrb_state *mrb, mrb_value val, mrb_int base)
 
   if (mrb_nil_p(val)) {
     if (base != 0) goto arg_error;
-      mrb_raise(mrb, E_TYPE_ERROR, "can't convert nil into Integer");
+    mrb_raise(mrb, E_TYPE_ERROR, "can't convert nil into Integer");
   }
   switch (mrb_type(val)) {
 #ifndef MRB_WITHOUT_FLOAT
     case MRB_TT_FLOAT:
       if (base != 0) goto arg_error;
-      else {
-        mrb_float f = mrb_float(val);
-        if (FIXABLE_FLOAT(f)) {
-          break;
-        }
-      }
       return mrb_flo_to_fixnum(mrb, val);
 #endif
 
@@ -568,11 +546,8 @@ mrb_convert_to_integer(mrb_state *mrb, mrb_value val, mrb_int base)
 arg_error:
     mrb_raise(mrb, E_ARGUMENT_ERROR, "base specified for non string value");
   }
-  tmp = convert_type(mrb, val, "Integer", "to_int", FALSE);
-  if (mrb_nil_p(tmp) || !mrb_fixnum_p(tmp)) {
-    tmp = mrb_to_integer(mrb, val, "to_i");
-  }
-  return tmp;
+  /* to raise TypeError */
+  return mrb_to_int(mrb, val);
 }
 
 MRB_API mrb_value
@@ -605,6 +580,67 @@ mrb_Float(mrb_state *mrb, mrb_value val)
 #endif
 
 MRB_API mrb_value
+mrb_to_str(mrb_state *mrb, mrb_value val)
+{
+  if (!mrb_string_p(val)) {
+    mrb_value type = inspect_type(mrb, val);
+    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S to String", type);
+  }
+  return val;
+}
+
+MRB_API mrb_value
+mrb_ensure_string_type(mrb_state *mrb, mrb_value str)
+{
+  if (!mrb_string_p(str)) {
+    mrb_raisef(mrb, E_TYPE_ERROR, "%S cannot be converted to String",
+               inspect_type(mrb, str));
+  }
+  return str;
+}
+
+MRB_API mrb_value
+mrb_check_string_type(mrb_state *mrb, mrb_value str)
+{
+  if (!mrb_string_p(str)) return mrb_nil_value();
+  return str;
+}
+
+MRB_API mrb_value
+mrb_ensure_array_type(mrb_state *mrb, mrb_value ary)
+{
+  if (!mrb_array_p(ary)) {
+    mrb_raisef(mrb, E_TYPE_ERROR, "%S cannot be converted to Array",
+               inspect_type(mrb, ary));
+  }
+  return ary;
+}
+
+MRB_API mrb_value
+mrb_check_array_type(mrb_state *mrb, mrb_value ary)
+{
+  if (!mrb_array_p(ary)) return mrb_nil_value();
+  return ary;
+}
+
+MRB_API mrb_value
+mrb_ensure_hash_type(mrb_state *mrb, mrb_value hash)
+{
+  if (!mrb_hash_p(hash)) {
+    mrb_raisef(mrb, E_TYPE_ERROR, "%S cannot be converted to Hash",
+               inspect_type(mrb, hash));
+  }
+  return hash;
+}
+
+MRB_API mrb_value
+mrb_check_hash_type(mrb_state *mrb, mrb_value hash)
+{
+  if (!mrb_hash_p(hash)) return mrb_nil_value();
+  return hash;
+}
+
+MRB_API mrb_value
 mrb_inspect(mrb_state *mrb, mrb_value obj)
 {
   return mrb_obj_as_string(mrb, mrb_funcall(mrb, obj, "inspect", 0));
diff --git a/src/string.c b/src/string.c
index b7abfb762..b6d4ecef0 100644
--- a/src/string.c
+++ b/src/string.c
@@ -956,15 +956,7 @@ str_eql(mrb_state *mrb, const mrb_value str1, const mrb_value str2)
 MRB_API mrb_bool
 mrb_str_equal(mrb_state *mrb, mrb_value str1, mrb_value str2)
 {
-  if (mrb_immediate_p(str2)) return FALSE;
-  if (!mrb_string_p(str2)) {
-    if (mrb_nil_p(str2)) return FALSE;
-    if (!mrb_respond_to(mrb, str2, mrb_intern_lit(mrb, "to_str"))) {
-      return FALSE;
-    }
-    str2 = mrb_funcall(mrb, str2, "to_str", 0);
-    return mrb_equal(mrb, str2, str1);
-  }
+  if (!mrb_string_p(str2)) return FALSE;
   return str_eql(mrb, str1, str2);
 }
 
@@ -992,14 +984,8 @@ mrb_str_equal_m(mrb_state *mrb, mrb_value str1)
 MRB_API mrb_value
 mrb_str_to_str(mrb_state *mrb, mrb_value str)
 {
-  mrb_value s;
-
   if (!mrb_string_p(str)) {
-    s = mrb_check_convert_type(mrb, str, MRB_TT_STRING, "String", "to_str");
-    if (mrb_nil_p(s)) {
-      s = mrb_convert_type(mrb, str, MRB_TT_STRING, "String", "to_s");
-    }
-    return s;
+    return mrb_convert_type(mrb, str, MRB_TT_STRING, "String", "to_s");
   }
   return str;
 }
@@ -1714,18 +1700,6 @@ mrb_ptr_to_str(mrb_state *mrb, void *p)
   return mrb_obj_value(p_str);
 }
 
-MRB_API mrb_value
-mrb_string_type(mrb_state *mrb, mrb_value str)
-{
-  return mrb_convert_type(mrb, str, MRB_TT_STRING, "String", "to_str");
-}
-
-MRB_API mrb_value
-mrb_check_string_type(mrb_state *mrb, mrb_value str)
-{
-  return mrb_check_convert_type(mrb, str, MRB_TT_STRING, "String", "to_str");
-}
-
 /* 15.2.10.5.30 */
 /*
  *  call-seq:
@@ -2379,7 +2353,6 @@ mrb_str_to_f(mrb_state *mrb, mrb_value self)
 /*
  *  call-seq:
  *     str.to_s     => str
- *     str.to_str   => str
  *
  *  Returns the receiver.
  */
@@ -2783,7 +2756,6 @@ mrb_init_string(mrb_state *mrb)
 #endif
   mrb_define_method(mrb, s, "to_i",            mrb_str_to_i,            MRB_ARGS_ANY());  /* 15.2.10.5.39 */
   mrb_define_method(mrb, s, "to_s",            mrb_str_to_s,            MRB_ARGS_NONE()); /* 15.2.10.5.40 */
-  mrb_define_method(mrb, s, "to_str",          mrb_str_to_s,            MRB_ARGS_NONE());
   mrb_define_method(mrb, s, "to_sym",          mrb_str_intern,          MRB_ARGS_NONE()); /* 15.2.10.5.41 */
   mrb_define_method(mrb, s, "upcase",          mrb_str_upcase,          MRB_ARGS_NONE()); /* 15.2.10.5.42 */
   mrb_define_method(mrb, s, "upcase!",         mrb_str_upcase_bang,     MRB_ARGS_NONE()); /* 15.2.10.5.43 */
diff --git a/test/t/string.rb b/test/t/string.rb
index e91b915fe..3a1eced16 100644
--- a/test/t/string.rb
+++ b/test/t/string.rb
@@ -253,19 +253,6 @@ assert('String#chomp!', '15.2.10.5.10') do
   assert_equal 'abc', e
 end
 
-assert('String#chomp! uses the correct length') do
-  class A
-    def to_str
-      $s.replace("AA")
-      "A"
-    end
-  end
-
-  $s = "AAA"
-  $s.chomp!(A.new)
-  assert_equal $s, "A"
-end
-
 assert('String#chop', '15.2.10.5.11') do
   a = ''.chop
   b = 'abc'.chop