diff --git a/assets/parser.d.erb b/assets/parser.d.erb
index c44fd22..c158be0 100644
--- a/assets/parser.d.erb
+++ b/assets/parser.d.erb
@@ -41,13 +41,13 @@ class <%= @classname %>
             uint code_point_length;
         }
 
-        static DecodedCodePoint decode_code_point(const(ubyte) * input, size_t input_length)
+        static DecodedCodePoint decode_code_point(string input)
         {
-            if (input_length == 0u)
+            if (input.length == 0u)
             {
                 return DecodedCodePoint(CODE_POINT_EOF, 0u);
             }
-            ubyte c = *input;
+            char c = input[0];
             uint code_point;
             uint code_point_length;
             if ((c & 0x80u) == 0u)
@@ -87,20 +87,19 @@ class <%= @classname %>
                 {
                     return DecodedCodePoint(CODE_POINT_INVALID, 0u);
                 }
-                if (input_length <= following_bytes)
+                if (input.length <= following_bytes)
                 {
                     return DecodedCodePoint(CODE_POINT_INVALID, 0u);
                 }
                 code_point_length = following_bytes + 1u;
-                while (following_bytes-- > 0u)
+                for (size_t i = 0u; i < following_bytes; i++)
                 {
-                    input++;
-                    ubyte b = *input;
-                    if ((b & 0xC0u) != 0u)
+                    char b = input[i + 1u];
+                    if ((b & 0xC0u) != 0x80u)
                     {
                         return DecodedCodePoint(CODE_POINT_INVALID, 0u);
                     }
-                    code_point = (code_point << 6u) | b;
+                    code_point = (code_point << 6u) | (b & 0x3Fu);
                 }
             }
             return DecodedCodePoint(code_point, code_point_length);
@@ -159,17 +158,15 @@ class <%= @classname %>
             uint token;
         }
 
-        private const(ubyte) * m_input;
-        private size_t m_input_length;
+        private string m_input;
         private size_t m_input_position;
         private size_t m_input_row;
         private size_t m_input_col;
         private size_t m_mode;
 
-        this(const(ubyte) * input, size_t input_length)
+        this(string input)
         {
             m_input = input;
-            m_input_length = input_length;
             m_mode = <%= @lexer.mode_id("default") %>;
         }
 
@@ -227,7 +224,7 @@ class <%= @classname %>
             uint current_state = modes[m_mode].state_table_offset;
             for (;;)
             {
-                auto decoded = Decoder.decode_code_point(&m_input[m_input_position + attempt_match_info.length], m_input_length - m_input_position - attempt_match_info.length);
+                auto decoded = Decoder.decode_code_point(m_input[(m_input_position + attempt_match_info.length)..(m_input.length)]);
                 if (decoded.code_point == Decoder.CODE_POINT_INVALID)
                 {
                     lt.token = _TOKEN_DECODE_ERROR;
@@ -377,9 +374,9 @@ class <%= @classname %>
 
         private <%= @grammar.result_type %> parse_result;
 
-        this(const(ubyte) * input, size_t input_length)
+        this(string input)
         {
-            m_lexer = new Lexer(input, input_length);
+            m_lexer = new Lexer(input);
         }
 
         bool parse()
diff --git a/spec/propane_spec.rb b/spec/propane_spec.rb
index bf8e816..e274543 100644
--- a/spec/propane_spec.rb
+++ b/spec/propane_spec.rb
@@ -76,6 +76,7 @@ EOF
     build_parser
     compile("spec/test_d_lexer.d")
     results = run
+    expect(results.stderr).to eq ""
     expect(results.status).to eq 0
   end
 
diff --git a/spec/test_d_lexer.d b/spec/test_d_lexer.d
index 5af56d8..92522bd 100644
--- a/spec/test_d_lexer.d
+++ b/spec/test_d_lexer.d
@@ -9,59 +9,27 @@ int main()
 unittest
 {
     alias DCP = Testparser.Decoder.DecodedCodePoint;
-    string inputstring = "5+\n 66";
-    const(ubyte) * input = cast(const(ubyte) *)inputstring.ptr;
-    size_t input_length = inputstring.length;
     DCP dcp;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
+
+    dcp = Testparser.Decoder.decode_code_point("5");
     assert(dcp == DCP('5', 1u));
-    input += dcp.code_point_length;
-    input_length -= dcp.code_point_length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
-    assert(dcp == DCP('+', 1u));
-    input += dcp.code_point_length;
-    input_length -= dcp.code_point_length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
-    assert(dcp == DCP('\n', 1u));
-    input += dcp.code_point_length;
-    input_length -= dcp.code_point_length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
-    assert(dcp == DCP(' ', 1u));
-    input += dcp.code_point_length;
-    input_length -= dcp.code_point_length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
-    assert(dcp == DCP('6', 1u));
-    input += dcp.code_point_length;
-    input_length -= dcp.code_point_length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
-    assert(dcp == DCP('6', 1u));
-    input += dcp.code_point_length;
-    input_length -= dcp.code_point_length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
+
+    dcp = Testparser.Decoder.decode_code_point("");
     assert(dcp == DCP(Testparser.Decoder.CODE_POINT_EOF, 0u));
 
-    inputstring = "\xf0\x1f\x27\x21";
-    input = cast(const(ubyte) *)inputstring.ptr;
-    input_length = inputstring.length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
+    dcp = Testparser.Decoder.decode_code_point("\xC2\xA9");
+    assert(dcp == DCP(0xA9u, 2u));
+
+    dcp = Testparser.Decoder.decode_code_point("\xf0\x9f\xa7\xa1");
     assert(dcp == DCP(0x1F9E1, 4u));
 
-    inputstring = "\xf0\x1f\x27";
-    input = cast(const(ubyte) *)inputstring.ptr;
-    input_length = inputstring.length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
+    dcp = Testparser.Decoder.decode_code_point("\xf0\x9f\x27");
     assert(dcp == DCP(Testparser.Decoder.CODE_POINT_INVALID, 0u));
 
-    inputstring = "\xf0\x1f\x27\xFF";
-    input = cast(const(ubyte) *)inputstring.ptr;
-    input_length = inputstring.length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
+    dcp = Testparser.Decoder.decode_code_point("\xf0\x9f\xa7\xFF");
     assert(dcp == DCP(Testparser.Decoder.CODE_POINT_INVALID, 0u));
 
-    inputstring = "\xfe";
-    input = cast(const(ubyte) *)inputstring.ptr;
-    input_length = inputstring.length;
-    dcp = Testparser.Decoder.decode_code_point(input, input_length);
+    dcp = Testparser.Decoder.decode_code_point("\xfe");
     assert(dcp == DCP(Testparser.Decoder.CODE_POINT_INVALID, 0u));
 }
 
@@ -69,7 +37,7 @@ unittest
 {
     alias LT = Testparser.Lexer.LexedToken;
     string input = "5 + 4 * \n677 + 567";
-    Testparser.Lexer lexer = new Testparser.Lexer(cast(const(ubyte) *)input.ptr, input.length);
+    Testparser.Lexer lexer = new Testparser.Lexer(input);
     assert(lexer.lex_token() == LT(0, 0, 1, Testparser.TOKEN_int));
     assert(lexer.lex_token() == LT(0, 2, 1, Testparser.TOKEN_plus));
     assert(lexer.lex_token() == LT(0, 4, 1, Testparser.TOKEN_int));
@@ -79,6 +47,6 @@ unittest
     assert(lexer.lex_token() == LT(1, 6, 3, Testparser.TOKEN_int));
     assert(lexer.lex_token() == LT(1, 9, 0, Testparser.TOKEN_0EOF));
 
-    lexer = new Testparser.Lexer(null, 0u);
+    lexer = new Testparser.Lexer("");
     assert(lexer.lex_token() == LT(0, 0, 0, Testparser.TOKEN_0EOF));
 }
diff --git a/spec/test_d_parser_identical_rules_lookahead.d b/spec/test_d_parser_identical_rules_lookahead.d
index 772711f..0b34a21 100644
--- a/spec/test_d_parser_identical_rules_lookahead.d
+++ b/spec/test_d_parser_identical_rules_lookahead.d
@@ -9,10 +9,10 @@ int main()
 unittest
 {
     string input = "aba";
-    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    auto parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
 
     input = "abb";
-    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
 }
diff --git a/spec/test_d_parser_rule_from_multiple_states.d b/spec/test_d_parser_rule_from_multiple_states.d
index 4b28ca8..8fff083 100644
--- a/spec/test_d_parser_rule_from_multiple_states.d
+++ b/spec/test_d_parser_rule_from_multiple_states.d
@@ -9,14 +9,14 @@ int main()
 unittest
 {
     string input = "a";
-    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    auto parser = new Testparser.Parser(input);
     assert(parser.parse() == false);
 
     input = "a b";
-    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
 
     input = "bb";
-    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
 }
diff --git a/spec/test_lexer_modes.d b/spec/test_lexer_modes.d
index c1f7b27..00000a1 100644
--- a/spec/test_lexer_modes.d
+++ b/spec/test_lexer_modes.d
@@ -9,12 +9,12 @@ int main()
 unittest
 {
     string input = `abc "a string" def`;
-    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    auto parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
     writeln("pass1");
 
     input = `abc "abc def" def`;
-    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
     writeln("pass2");
 }
diff --git a/spec/test_parser_rule_user_code.d b/spec/test_parser_rule_user_code.d
index 5829f74..9b0b503 100644
--- a/spec/test_parser_rule_user_code.d
+++ b/spec/test_parser_rule_user_code.d
@@ -9,6 +9,6 @@ int main()
 unittest
 {
     string input = "ab";
-    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    auto parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
 }
diff --git a/spec/test_parsing_lists.d b/spec/test_parsing_lists.d
index 71df9e5..297891c 100644
--- a/spec/test_parsing_lists.d
+++ b/spec/test_parsing_lists.d
@@ -9,17 +9,17 @@ int main()
 unittest
 {
     string input = "a";
-    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    auto parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
     assert(parser.result == 1u);
 
     input = "";
-    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
     assert(parser.result == 0u);
 
     input = "aaaaaaaaaaaaaaaa";
-    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
     assert(parser.result == 16u);
 }
diff --git a/spec/test_pattern.d b/spec/test_pattern.d
index aba9195..d8c160d 100644
--- a/spec/test_pattern.d
+++ b/spec/test_pattern.d
@@ -9,12 +9,12 @@ int main()
 unittest
 {
     string input = "abcdef";
-    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    auto parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
     writeln("pass1");
 
     input = "defabcdef";
-    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
     writeln("pass2");
 }
diff --git a/spec/test_return_token_from_pattern.d b/spec/test_return_token_from_pattern.d
index 970e0d1..66a755f 100644
--- a/spec/test_return_token_from_pattern.d
+++ b/spec/test_return_token_from_pattern.d
@@ -9,6 +9,6 @@ int main()
 unittest
 {
     string input = "defghidef";
-    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    auto parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
 }
diff --git a/spec/test_user_code.d b/spec/test_user_code.d
index ad3fd25..719065a 100644
--- a/spec/test_user_code.d
+++ b/spec/test_user_code.d
@@ -9,12 +9,12 @@ int main()
 unittest
 {
     string input = "abcdef";
-    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    auto parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
     writeln("pass1");
 
     input = "abcabcdef";
-    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    parser = new Testparser.Parser(input);
     assert(parser.parse() == true);
     writeln("pass2");
 }