Add LazyFactory class

This class eliminates the need for auxiliary variables (prefixed
with '_') associated to lazy-initialized properties.

Change-Id: Ie2899151f4c70a3532923dcacb1debcd01509c97
Reviewed-by: Karsten Heimrich <karsten.heimrich@qt.io>

3 files changed, 62 insertions, 3 deletions

diff --git a/QtVsTools.Core/Common/EnumExt.cs b/QtVsTools.Core/Common/EnumExt.cs
index d7e705d6..f685267b 100644
--- a/QtVsTools.Core/Common/EnumExt.cs
+++ b/QtVsTools.Core/Common/EnumExt.cs
@@ -40,6 +40,8 @@ namespace QtVsTools.Common
     /// </summary>
     public static class EnumExt
     {
+        static LazyFactory StaticLazy { get; } = new LazyFactory();
+
         /// <summary>
         /// Wrapper for enum cast values.
         /// </summary>
@@ -200,15 +202,14 @@ namespace QtVsTools.Common
                 .FirstOrDefault();
         }
 
-        static IEnumerable<Type> _CastAttribTypes;
         /// <summary>
         /// List of cast attribute types.
         /// </summary>
         /// <remarks>
         /// Future cast attribute types need to be added to this list.
         /// </remarks>
-        static IEnumerable<Type> CastAttribTypes => _CastAttribTypes
-            ?? (_CastAttribTypes = new[]
+        static IEnumerable<Type> CastAttribTypes => StaticLazy.Get(() =>
+            CastAttribTypes, () => new[]
             {
                 typeof(StringAttribute)
             });
diff --git a/QtVsTools.Core/Common/LazyFactory.cs b/QtVsTools.Core/Common/LazyFactory.cs
new file mode 100644
index 00000000..93d096c4
--- /dev/null
+++ b/QtVsTools.Core/Common/LazyFactory.cs
@@ -0,0 +1,57 @@
+/****************************************************************************
+**
+** Copyright (C) 2022 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt VS Tools.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+using System;
+using System.Collections.Concurrent;
+using System.Diagnostics;
+using System.Linq.Expressions;
+using System.Reflection;
+
+namespace QtVsTools.Common
+{
+    public class LazyFactory
+    {
+        private Lazy<ConcurrentDictionary<PropertyInfo, Lazy<object>>> LazyObjs { get; }
+        private ConcurrentDictionary<PropertyInfo, Lazy<object>> Objs => LazyObjs.Value;
+
+        public LazyFactory()
+        {
+            LazyObjs = new Lazy<ConcurrentDictionary<PropertyInfo, Lazy<object>>>();
+        }
+
+        public T Get<T>(Expression<Func<T>> propertyRef, Func<T> initFunc) where T : class
+        {
+            var lazyPropertyExpr = propertyRef?.Body as MemberExpression;
+            var lazyProperty = lazyPropertyExpr?.Member as PropertyInfo;
+            if (lazyProperty == null)
+                throw new ArgumentException("Invalid property reference", "propertyRef");
+            var lazyObj = Objs.GetOrAdd(lazyProperty, (_) => new Lazy<object>(() => initFunc()));
+            return lazyObj.Value as T;
+        }
+    }
+}
diff --git a/QtVsTools.Core/QtVsTools.Core.csproj b/QtVsTools.Core/QtVsTools.Core.csproj
index 9ac5f6fa..dd20d370 100644
--- a/QtVsTools.Core/QtVsTools.Core.csproj
+++ b/QtVsTools.Core/QtVsTools.Core.csproj
@@ -124,6 +124,7 @@
     <Compile Include="BuildConfig.cs" />
     <Compile Include="CommandLineParser.cs" />
     <Compile Include="Common\EnumExt.cs" />
+    <Compile Include="Common\LazyFactory.cs" />
     <Compile Include="CompilerToolWrapper.cs" />
     <Compile Include="CxxStreamReader.cs" />
     <Compile Include="ExportProjectDialog.cs">