merged conflict: Performance improvement for most common usage

Author: psoholt

VerbalExpressions/RegexCache.cs

@@ -0,0 +1,62 @@
+using System;
+using System.Text.RegularExpressions;
+
+namespace CSharpVerbalExpressions
+{
+    public sealed class RegexCache
+    {
+        private bool hasValue;
+        private Key key;
+        private Regex regex;
+        
+        private class Key
+        {
+            public Key(string pattern, RegexOptions options)
+            {
+                this.Pattern = pattern;
+                this.Options = options;
+            }
+
+            public string Pattern { get; private set; }
+            public RegexOptions Options { get; private set; }
+            
+            public override bool Equals(object obj)
+            {
+                var key = obj as Key;
+                return key != null &&
+                       key.Pattern == this.Pattern &&
+                       key.Options == this.Options;
+            }
+
+            public override int GetHashCode()
+            {
+                return this.Pattern.GetHashCode() ^ this.Options.GetHashCode();
+            }
+        }
+
+        /// <summary>
+        /// Gets the already cached value for a key, or calculates the value and stores it.
+        /// </summary>
+        /// <param name="pattern">The pattern used to create the regular expression.</param>
+        /// <param name="options">The options for regex.</param>
+        /// <returns>The calculated or cached value.</returns>
+        public Regex Get(string pattern, RegexOptions options)
+        {
+            if (pattern == null) throw new ArgumentNullException("pattern");
+
+            lock (this)
+            {
+                var current = new Key(pattern, options);
+                if (this.hasValue && current.Equals(this.key))
+                {
+                    return this.regex;
+                }
+
+                this.regex = new Regex(pattern, options);
+                this.key = current;
+                this.hasValue = true;
+                return this.regex;
+            }
+        }
+    }
+}