To accurate `pos`

pos shouldn't cache because it's not controllable

mrblib/io.rb

@@ -124,7 +124,6 @@ class IO
     str = string.is_a?(String) ? string : string.to_s
     return str.size unless str.size > 0
     len = syswrite(str)
-    @pos += len
     len
   end
 
@@ -146,7 +145,7 @@ class IO
 
   def pos
     raise IOError if closed?
-    @pos
+    sysseek(0, SEEK_CUR) - @buf.length
   end
   alias_method :tell, :pos
 
@@ -160,7 +159,7 @@ class IO
 
   def seek(i, whence = SEEK_SET)
     raise IOError if closed?
-    @pos = sysseek(i, whence)
+    sysseek(i, whence)
     @buf = ''
     0
   end
@@ -172,7 +171,6 @@ class IO
 
   def ungetc(substr)
     raise TypeError.new "expect String, got #{substr.class}" unless substr.is_a?(String)
-    @pos -= substr.size
     if @buf.empty?
       @buf = substr.dup
     else
@@ -195,7 +193,6 @@ class IO
     end
 
     array = []
-    start_pos = @pos
     while 1
       begin
         _read_buf
@@ -204,15 +201,12 @@ class IO
         break
       end
 
-      if length && (@pos - start_pos + @buf.size) >= length
-        len = length - (@pos - start_pos)
-        array.push @buf[0, len]
-        @pos += len
-        @buf = @buf[len, @buf.size - len]
+      if length && length <= @buf.size
+        array.push @buf[0, length]
+        @buf = @buf[length, @buf.size - length]
         break
       else
         array.push @buf
-        @pos += @buf.size
         @buf = ''
       end
     end
@@ -240,7 +234,6 @@ class IO
     end
 
     array = []
-    start_pos = @pos
     while 1
       begin
         _read_buf
@@ -249,21 +242,17 @@ class IO
         break
       end
 
-      if limit && (@pos - start_pos + @buf.size) >= limit
-        len = limit - (@pos - start_pos)
-        array.push @buf[0, len]
-        @pos += len
-        @buf = @buf[len, @buf.size - len]
+      if limit && limit <= @buf.size
+        array.push @buf[0, limit]
+        @buf = @buf[limit, @buf.size - limit]
         break
       elsif idx = @buf.index(rs)
         len = idx + rs.size
         array.push @buf[0, len]
-        @pos += len
         @buf = @buf[len, @buf.size - len]
         break
       else
         array.push @buf
-        @pos += @buf.size
         @buf = ''
       end
     end
@@ -285,7 +274,6 @@ class IO
     _read_buf
     c = @buf[0]
     @buf = @buf[1, @buf.size]
-    @pos += 1
     c
   end
 

src/io.c

@@ -389,7 +389,6 @@ mrb_io_s_popen(mrb_state *mrb, mrb_value klass)
       }
 
       mrb_iv_set(mrb, io, mrb_intern_cstr(mrb, "@buf"), mrb_str_new_cstr(mrb, ""));
-      mrb_iv_set(mrb, io, mrb_intern_cstr(mrb, "@pos"), mrb_fixnum_value(0));
 
       fptr = mrb_io_alloc(mrb);
       fptr->fd = fd;
@@ -443,7 +442,6 @@ mrb_io_initialize(mrb_state *mrb, mrb_value io)
   flags = mrb_io_modestr_to_flags(mrb, mrb_string_value_cstr(mrb, &mode));
 
   mrb_iv_set(mrb, io, mrb_intern_cstr(mrb, "@buf"), mrb_str_new_cstr(mrb, ""));
-  mrb_iv_set(mrb, io, mrb_intern_cstr(mrb, "@pos"), mrb_fixnum_value(0));
 
   fptr = (struct mrb_io *)DATA_PTR(io);
   if (fptr != NULL) {
@@ -801,7 +799,6 @@ mrb_io_s_pipe(mrb_state *mrb, mrb_value klass)
 
   r = mrb_obj_value(mrb_data_object_alloc(mrb, mrb_class_ptr(klass), NULL, &mrb_io_type));
   mrb_iv_set(mrb, r, mrb_intern_cstr(mrb, "@buf"), mrb_str_new_cstr(mrb, ""));
-  mrb_iv_set(mrb, r, mrb_intern_cstr(mrb, "@pos"), mrb_fixnum_value(0));
   fptr_r = mrb_io_alloc(mrb);
   fptr_r->fd = pipes[0];
   fptr_r->readable = 1;
@@ -812,7 +809,6 @@ mrb_io_s_pipe(mrb_state *mrb, mrb_value klass)
 
   w = mrb_obj_value(mrb_data_object_alloc(mrb, mrb_class_ptr(klass), NULL, &mrb_io_type));
   mrb_iv_set(mrb, w, mrb_intern_cstr(mrb, "@buf"), mrb_str_new_cstr(mrb, ""));
-  mrb_iv_set(mrb, w, mrb_intern_cstr(mrb, "@pos"), mrb_fixnum_value(0));
   fptr_w = mrb_io_alloc(mrb);
   fptr_w->fd = pipes[1];
   fptr_w->readable = 0;