Cache the current working directory.

lib/path.dart

 // Copyright (c) 2012, 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.
 
 /// A comprehensive, cross-platform path manipulation library.
 ///
 /// ## Installing ##
 ///
 /// Use [pub][] to install this package. Add the following to your
 /// `pubspec.yaml` file.
@@ skipping 61 matching lines @@
 /// Returns the [Style] of the current context.
 ///
 /// This is the style that all top-level path functions will use.
 Style get style => context.style;
 
 /// Gets the path to the current working directory.
 ///
 /// In the browser, this means the current URL, without the last file segment.
 String get current {
   var uri = Uri.base;
+
+  // Converting the base URI to a file path is pretty slow, and the base URI
+  // rarely changes in practice, so we cache the result here.
+  if (uri == _currentUriBase) return _current;
+  _currentUriBase = uri;
+
   if (Style.platform == Style.url) {
-    return uri.resolve('.').toString();
+    _current = uri.resolve('.').toString();

[Lasse Reichstein Nielsen, 2015/12/01 06:52:58]

That is likely to be slower than necessary.
Instead maybe:
   var path = uri.path;
   if (path.length > 1) {
     uri = uri.replace(path: uri.path.substring(0, path.length - 1));
   }
  _current = uri.toString)(;
(That is likely to be faster, but not guaranteed, since you still reparse the
path, but you avoid the complexity of dot-normalizing a path).

[Lasse Reichstein Nielsen, 2015/12/01 06:53:54]

(That does assume that Uri.base has no query or fragment, so maybe it's not
general enough).

[nweiz, 2015/12/01 20:50:46]

Given that this is cached now, I think it's probably not worth putting a lot of
effort into optimizing the code to compute the cached value.

+    return _current;
   } else {
     var path = uri.toFilePath();
     // Remove trailing '/' or '\'.
-    int lastIndex = path.length - 1;
+    var lastIndex = path.length - 1;
     assert(path[lastIndex] == '/' || path[lastIndex] == '\\');
-    return path.substring(0, lastIndex);
+    _current = path.substring(0, lastIndex);
+    return _current;
   }
 }
 
+/// The last value returned by [Uri.base].
+///
+/// This is used to cache the current working directory.
+Uri _currentUriBase;
+
+/// The last known value of the current working directory.
+///
+/// This is cached because [current] is called frequently but rarely actually
+/// changes.
+String _current;
+
 /// Gets the path separator for the current platform. This is `\` on Windows
 /// and `/` on other platforms (including the browser).
 String get separator => context.separator;
 
 /// Creates a new path by appending the given path parts to [current].
 /// Equivalent to [join()] with [current] as the first argument. Example:
 ///
 ///     path.absolute('path', 'to/foo'); // -> '/your/current/dir/path/to/foo'
 String absolute(String part1, [String part2, String part3, String part4,
     String part5, String part6, String part7]) =>
@@ skipping 269 matching lines @@
 ///
 ///     // Windows at "C:\root\path"
 ///     path.prettyUri('file:///C:/root/path/a/b.dart'); // -> r'a\b.dart'
 ///     path.prettyUri('http://dartlang.org/'); // -> 'http://dartlang.org'
 ///
 ///     // URL at "http://dartlang.org/root/path"
 ///     path.prettyUri('http://dartlang.org/root/path/a/b.dart');
 ///         // -> r'a/b.dart'
 ///     path.prettyUri('file:///root/path'); // -> 'file:///root/path'
 String prettyUri(uri) => context.prettyUri(uri);