Improve scanner performance by remembering string's CharAt function as the string type does not cha…

runtime/vm/scanner.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Scanner class for the Dart language. The scanner reads source text
 // and produces a stream of tokens which is used by the parser.
 //
 
 #ifndef VM_SCANNER_H_
 #define VM_SCANNER_H_
 
 #include "vm/growable_array.h"
 #include "vm/token.h"
 
 namespace dart {
 
 // Forward declarations.
 class Array;
 class Library;
 class RawString;
 class String;
 
 // A call to Scan() scans the source one token at at time.
 // The scanned token is returned by cur_token().
 // GetStream() scans the entire source text and returns a stream of tokens.
 class Scanner : ValueObject {
  public:
+  typedef int32_t (*CharAtFunc)(const String& str, intptr_t index);
+
   // SourcePosition describes a text location in user friendly
   // terms of line number and column.
   struct SourcePosition {
     int line;
     int column;
   };
 
   // TokenDesc defines the kind of a token and its location in
   // the source text.
   struct TokenDescriptor {
@@ skipping 30 matching lines @@
   bool NewlineBeforeToken() const { return newline_seen_; }
 
   // Source code line number and column of current token.
   const SourcePosition& CurrentPosition() const {
     return current_token_.position;
   }
 
   static void InitOnce();
 
   // Return true if str is an identifier.
-  static bool IsIdent(const String& str);
+  bool IsIdent(const String& str);
 
   // Does the token stream contain a valid literal. This is used to implement
   // the Dart methods int.parse and double.parse.
   static bool IsValidLiteral(const Scanner::GrowableTokenStream& tokens,
                              Token::Kind literal_kind,
                              bool* is_positive,
                              const String** value);
 
  private:
   static const int kNumLowercaseChars = 26;
@@ skipping 86 matching lines @@
   }
   void ScanIdentNoDollar() {
     ScanIdentChars(false);
   }
 
   // Reads a number literal.
   void ScanNumber(bool dec_point_seen);
 
   void ScanScriptTag();
 
+  CharAtFunc CallCharAt() const { return char_at_func_; }
+
   static void PrintTokens(const GrowableTokenStream& ts);
 
   TokenDescriptor current_token_;  // Current token.
   TokenDescriptor newline_token_;  // Newline token.
   TokenDescriptor empty_string_token_;  // Token for "".
   const String& source_;           // The source text being tokenized.
   intptr_t source_length_;         // The length of the source text.
   intptr_t lookahead_pos_;         // Position of lookahead character
                                    // within source_.
   intptr_t token_start_;           // Begin of current token in src_.
   int32_t c0_;                     // Lookahead character.
   bool newline_seen_;              // Newline before current token.
   intptr_t prev_token_line_;       // Line number of the previous token.
 
   // The following fields keep track whether we are scanning a string literal
   // and its interpolated expressions.
   ScanContext* saved_context_;
   int32_t string_delimiter_;
   bool string_is_multiline_;
   int brace_level_;
 
   const String& private_key_;
 
   SourcePosition c0_pos_;      // Source position of lookahead character c0_.
 
+  const CharAtFunc char_at_func_;
+
   static KeywordTable keywords_[Token::kNumKeywords];
   static int keywords_char_offset_[kNumLowercaseChars];
 };
 
 
 }  // namespace dart
 
 #endif  // VM_SCANNER_H_