StyletIoC: Don't cache expressions by default

This in turn causes ConstructorInfos to be cached, and those are pretty
expensive.

Stylet/StyletIoC/Internal/Creators/TypeCreator.cs

@@ -109,8 +109,15 @@ namespace StyletIoC.Internal.Creators
 
             var completeExpression = this.CompleteExpressionFromCreator(creator, registrationContext);
 
-            Interlocked.CompareExchange(ref this.creationExpression, completeExpression, null);
-            return this.creationExpression;
+            if (StyletIoCContainer.CacheGeneratedExpressions)
+            {
+                Interlocked.CompareExchange(ref this.creationExpression, completeExpression, null);
+                return this.creationExpression;
+            }
+            else
+            {
+                return completeExpression;
+            }
         }
     }
 }

Stylet/StyletIoC/Internal/Registrations/GetAllRegistration.cs

@@ -60,8 +60,15 @@ namespace StyletIoC.Internal.Registrations
             var listNew = Expression.New(listCtor, Expression.Constant(instanceExpressions.Length));
             Expression list = instanceExpressions.Any() ? (Expression)Expression.ListInit(listNew, instanceExpressions) : listNew;
 
-            Interlocked.CompareExchange(ref this.expression, list, null);
-            return this.expression;
+            if (StyletIoCContainer.CacheGeneratedExpressions)
+            {
+                Interlocked.CompareExchange(ref this.expression, list, null);
+                return this.expression;
+            }
+            else
+            {
+                return list;
+            }
         }
     }
 }

Stylet/StyletIoC/StyletIoCContainer.cs

@@ -11,5 +11,17 @@ namespace StyletIoC
         /// Name of the assembly in which abstract factories are built. Use in [assembly: InternalsVisibleTo(StyletIoCContainer.FactoryAssemblyName)] to allow factories created by .ToAbstractFactory() to access internal types
         /// </summary>
         public static readonly string FactoryAssemblyName = "StyletIoCFactory";
+
+        /// <summary>
+        /// Gets or sets a value indicating whether generated Expressions are cached, or resolved anew each time.
+        /// Setting to true may speed up the compilation phase in the case where one type is required by many other types.
+        /// However, it will cause loads of ConstructorInfos to be cached forever, and they're actually pretty expensive to hold on to.
+        /// </summary>
+        public static bool CacheGeneratedExpressions { get; set; }
+
+        static StyletIoCContainer()
+        {
+            CacheGeneratedExpressions = false;
+        }
     }
 }