- Remove scanning by regular expression and redundant scanning.

lib/src/loader.dart

Index: lib/src/loader.dart
diff --git a/lib/src/loader.dart b/lib/src/loader.dart
index 07929579c14654eafceaa702faf0acd7dc643d5a..e1a59e1409bf0c15b3aaeb7fd986e1301d5a3763 100644
--- a/lib/src/loader.dart
+++ b/lib/src/loader.dart
@@ -13,30 +13,10 @@ import 'yaml_document.dart';
 import 'yaml_exception.dart';
 import 'yaml_node.dart';
 
-/// Matches YAML null.
-final _nullRegExp = new RegExp(r"^(null|Null|NULL|~|)$");
-
-/// Matches a YAML bool.
-final _boolRegExp = new RegExp(r"^(?:(true|True|TRUE)|(false|False|FALSE))$");
-
-/// Matches a YAML decimal integer like `+1234`.
-final _decimalIntRegExp = new RegExp(r"^[-+]?[0-9]+$");
-
-/// Matches a YAML octal integer like `0o123`.
-final _octalIntRegExp = new RegExp(r"^0o([0-7]+)$");
-
-/// Matches a YAML hexidecimal integer like `0x123abc`.
-final _hexIntRegExp = new RegExp(r"^0x[0-9a-fA-F]+$");
-
-/// Matches a YAML floating point number like `12.34+e56`.
-final _floatRegExp = new RegExp(
-    r"^[-+]?(\.[0-9]+|[0-9]+(\.[0-9]*)?)([eE][-+]?[0-9]+)?$");
-
-/// Matches YAML infinity.
-final _infinityRegExp = new RegExp(r"^([+-]?)\.(inf|Inf|INF)$");
-
-/// Matches YAML NaN.
-final _nanRegExp = new RegExp(r"^\.(nan|NaN|NAN)$");
+// A singleton class which corresponds to no value having been scanned.
+class _NoValue {
+  const _NoValue();
+}
 
 /// A loader that reads [Event]s emitted by a [Parser] and emits
 /// [YamlDocument]s.
@@ -133,15 +113,11 @@ class Loader {
   YamlNode _loadScalar(ScalarEvent scalar) {
     var node;
     if (scalar.tag == "!") {
-      node = _parseString(scalar);
+      node = new YamlScalar.internal(scalar.value, scalar.span, scalar.style);
     } else if (scalar.tag != null) {
-      node = _parseByTag(scalar);
+      node = _scanByTag(scalar);
     } else {
-      node = _parseNull(scalar);
-      if (node == null) node = _parseBool(scalar);
-      if (node == null) node = _parseInt(scalar);
-      if (node == null) node = _parseFloat(scalar);
-      if (node == null) node = _parseString(scalar);
+      node = _scanScalar(scalar);
     }
 
     _registerAnchor(scalar.anchor, node);
@@ -194,85 +170,189 @@ class Loader {
     return node;
   }
 
+  // Value returned by the scanning functions if no valid value was scanned.
+  static const _kNoValue = const _NoValue();
+
   /// Parses a scalar according to its tag name.
-  YamlScalar _parseByTag(ScalarEvent scalar) {
+  YamlScalar _scanByTag(ScalarEvent scalar) {
+    var str = scalar.value;
+    var len = str.length;
+    var ch0 = (len == 0) ? null : str.codeUnitAt(0);
+
+    var value = _kNoValue;
     switch (scalar.tag) {
-      case "tag:yaml.org,2002:null": return _parseNull(scalar);
-      case "tag:yaml.org,2002:bool": return _parseBool(scalar);
-      case "tag:yaml.org,2002:int": return _parseInt(scalar);
-      case "tag:yaml.org,2002:float": return _parseFloat(scalar);
-      case "tag:yaml.org,2002:str": return _parseString(scalar);
+      case "tag:yaml.org,2002:null":
+        value = _scanNull(str, ch0, len);
+        break;
+      case "tag:yaml.org,2002:bool":
+        value = _scanBool(str, ch0, len);
+        break;
+      case "tag:yaml.org,2002:int":
+        value = _scanNumber(str, ch0, len, true, false);
+        break;
+      case "tag:yaml.org,2002:float":
+        value = _scanNumber(str, ch0, len, false, true);
+        break;
+      case "tag:yaml.org,2002:str":
+        value = str;
+        break;
+      default:
+        throw new YamlException('Undefined tag: ${scalar.tag}.', scalar.span);
+    }
+    if (value != _kNoValue) {
+      return new YamlScalar.internal(value, scalar.span, scalar.style);
     }
-    throw new YamlException('Undefined tag: ${scalar.tag}.', scalar.span);
+    return null;
   }
 
-  /// Parses a null scalar.
-  YamlScalar _parseNull(ScalarEvent scalar) {
-    // TODO(nweiz): add ScalarStyle and implicit metadata to the scalars.
-    if (_nullRegExp.hasMatch(scalar.value)) {
-      return new YamlScalar.internal(null, scalar.span, scalar.style);
+  /// Code unit values.
+  static const _plus = 0x2B;
+  static const _minus = 0x2D;
+  static const _dot = 0x2E;
+  static const _0 = 0x30;
+  static const _9 = 0x39;
+  static const _F = 0x46;
+  static const _N = 0x4E;
+  static const _T = 0x54;
+  static const _f = 0x66;
+  static const _n = 0x6E;
+  static const _o = 0x6F;
+  static const _t = 0x74;
+  static const _x = 0x78;
+  static const _tilde = 0x7E;
+
+  /// Scan a scalar event's value.
+  YamlScalar _scanScalar(ScalarEvent scalar) {
+    final str = scalar.value;
+    final len = str.length;
+    final span = scalar.span;
+    final style = scalar.style;
+
+    var value = _kNoValue;
+
+    // Quickly check for the empty string.
+    if (len == 0) {
+      // Empty string is equivalent to null.
+      value = null;
     } else {
-      return null;
+      // Dispatch on the first character.
+      var ch0 = str.codeUnitAt(0);
+      if ((ch0 == _dot) || (ch0 == _plus) || (ch0 == _minus) ||
+          ((ch0 >= _0) && (ch0 <= _9))) {
+        // Recognize numbers (either int or double).
+        value = _scanNumber(str, ch0, len, true, true);
+      } else if ((len == 4) && ((ch0 == _n) || (ch0 == _N))) {
+        value = _scanNull(str, ch0, len);
+      } else if (((len == 4) && ((ch0 == _t) || (ch0 == _T))) ||
+                 ((len == 5) && ((ch0 == _f) || (ch0 == _F)))) {
+        value = _scanBool(str, ch0, len);
+      } else if ((len == 1) && (ch0 == _tilde)) {
+        // Special case of null be written as "~'.
+        value = null;
+      }
     }
-  }
 
-  /// Parses a boolean scalar.
-  YamlScalar _parseBool(ScalarEvent scalar) {
-    var match = _boolRegExp.firstMatch(scalar.value);
-    if (match == null) return null;
-    return new YamlScalar.internal(
-        match.group(1) != null, scalar.span, scalar.style);
-  }
-
-  /// Parses an integer scalar.
-  YamlScalar _parseInt(ScalarEvent scalar) {
-    var match = _decimalIntRegExp.firstMatch(scalar.value);
-    if (match != null) {
-      return new YamlScalar.internal(
-          int.parse(match.group(0)), scalar.span, scalar.style);
+    // If no value was found, set to the String value.
+    if (value == _kNoValue) {
+      value = str;
     }
+    return new YamlScalar.internal(value, span, style);
+  }
 
-    match = _octalIntRegExp.firstMatch(scalar.value);
-    if (match != null) {
-      var n = int.parse(match.group(1), radix: 8);
-      return new YamlScalar.internal(n, scalar.span, scalar.style);
+  /// Scan the different versions of the null literal.
+  _scanNull(String str, int ch0, int len) {
+    if (len == 4) {
+      if (((ch0 == _n) && (str == "null")) ||
+          ((ch0 == _N) && ((str == "Null") || (str == "NULL")))) {
+        return null;
+      }
+    } else if ((len == 0) || ((len == 1) && (ch0 == _tilde))) {
+      return null;
     }
+    return _kNoValue;
+  }
 
-    match = _hexIntRegExp.firstMatch(scalar.value);
-    if (match != null) {
-      return new YamlScalar.internal(
-          int.parse(match.group(0)), scalar.span, scalar.style);
+  /// Scan a boolean.
+  _scanBool(String str, int ch0, int len) {
+    if (len == 4) {
+      if (((ch0 == _t) && (str == "true")) ||
+          ((ch0 == _T) && ((str == "True") || (str == "TRUE")))) {
+        return true;
+      }
+    } else if (len == 5) {
+      if (((ch0 == _f) && (str == "false")) ||
+          ((ch0 == _F) && ((str == "False") || (str == "FALSE")))) {
+        return false;
+      }
     }
-
-    return null;
+    return _kNoValue;
   }
 
-  /// Parses a floating-point scalar.
-  YamlScalar _parseFloat(ScalarEvent scalar) {
-    var match = _floatRegExp.firstMatch(scalar.value);
-    if (match != null) {
-      // YAML allows floats of the form "0.", but Dart does not. Fix up those
-      // floats by removing the trailing dot.
-      var matchStr = match.group(0).replaceAll(new RegExp(r"\.$"), "");
-      return new YamlScalar.internal(
-          double.parse(matchStr), scalar.span, scalar.style);
-    }
 
-    match = _infinityRegExp.firstMatch(scalar.value);
-    if (match != null) {
-      var value = match.group(1) == "-" ? -double.INFINITY : double.INFINITY;
-      return new YamlScalar.internal(value, scalar.span, scalar.style);
-    }
+  /// Helper which returns the known "no value" when number parsing fails.
+  static var _onNumError = (_) => null;
 
-    match = _nanRegExp.firstMatch(scalar.value);
-    if (match != null) {
-      return new YamlScalar.internal(double.NAN, scalar.span, scalar.style);
+  /// Scan a number. Handles both integers and floats within one function if
+  /// possible avoid rescanning in the general case.
+  _scanNumber(String str, int ch0, int len, bool allow_int, bool allow_float) {
+    // Quick check for single digit integers.
+    if (len == 1) {
+      var val = ch0 - _0;
+      if ((val >= 0) && (val <= 9)) {
+        return val;
+      }
+      return _kNoValue;
     }
-
-    return null;
+    // Assume we are scanning a nicely formed number.
+    var ch1 = str.codeUnitAt(1);
+    if (allow_int && (ch0 == _0) && ((ch1 == _x) || (ch1 == _o))) {
+      // Scanning hex or octal integers.
+      var sub_str = str.substring(2);
+      if (ch1 == _x) {
+        var result = int.parse(sub_str, radix:16, onError: _onNumError);
+        return (result != null) ? result : _kNoValue;
+      }
+      var result = int.parse(sub_str, radix: 8, onError: _onNumError);
+      return (result != null) ? result : _kNoValue;
+    } else if (((ch0 >= _0) && (ch0 <= _9)) ||
+               (((ch0 == _plus) || (ch0 == _minus)) &&
+                (ch1 >= _0) && (ch1 <= _9))) {
+      // Either starting with a number or starting with a sign and number.
+      var result = null;
+      if (allow_int) {
+        // Possible hex or octal numbers are handled above, so only allow
+        // radix 10 here.
+        result = int.parse(str, radix: 10, onError: _onNumError);
+      }
+      // If we failed to scan an int, try to scan as a double.
+      if (allow_float && (result == null)) {
+        result = double.parse(str, _onNumError);
+      }
+      return (result != null) ? result : _kNoValue;
+    } else if (allow_float) {
+      // Not the only possibility is to scan a float starting with a dot or
+      // a sign and a dot. As well as the signed/unsigned infinity values and
+      // not-a-numbers.
+      if (((ch0 == _dot) && (ch1 >= _0) && (ch1 <= _9)) ||
+          ((ch0 == _minus) || (ch0 == _plus)) && (ch1 == _dot)) {
+        // Starting with a . and a number or a sign followed by a dot.
+        if (len == 5) {
+          if (str == "+.inf" || str == "+.Inf" || str == "+.INF") {
+            return double.INFINITY;
+          } else if (str == "-.inf" || str == "-.Inf" || str == "-.INF") {
+            return -double.INFINITY;
+          }
+        }
+        var result = double.parse(str, _onNumError);
+        return (result != null) ? result : _kNoValue;
+      } else if ((len == 4) && (ch0 == _dot)) {
+        if (str == ".inf" || str == ".Inf" || str == ".INF") {
+          return double.INFINITY;
+        } else if (str == ".nan" || str == ".NaN" || str == ".NAN") {
+          return double.NAN;
+        }
+      }
+    }
+    return _kNoValue;
   }
-
-  /// Parses a string scalar.
-  YamlScalar _parseString(ScalarEvent scalar) =>
-      new YamlScalar.internal(scalar.value, scalar.span, scalar.style);
 }