From a7ca007e24c32e8408bc8ceb3a745e3a7469f9a2 Mon Sep 17 00:00:00 2001
From: John Maguire <john.maguire@gmail.com>
Date: Thu, 11 Feb 2016 14:09:36 +0000
Subject: [PATCH] Tidy up lazy implementation.

---
 ext/libclementine-common/core/lazy.h | 44 +++++++++++++++++++++++-----
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/ext/libclementine-common/core/lazy.h b/ext/libclementine-common/core/lazy.h
index 43684891c..caf4235fb 100644
--- a/ext/libclementine-common/core/lazy.h
+++ b/ext/libclementine-common/core/lazy.h
@@ -1,25 +1,55 @@
+/* This file is part of Clementine.
+   Copyright 2016, John Maguire <john.maguire@gmail.com>
+
+   Clementine is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   Clementine is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with Clementine.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef LAZY_H
+#define LAZY_H
+
 #include <functional>
 #include <memory>
 
+// Helper for lazy initialisation of objects.
+// Usage:
+//    Lazy<Foo> my_lazy_object([]() { return new Foo; });
 template <typename T>
 class Lazy {
  public:
   explicit Lazy(std::function<T*()> init) : init_(init) {}
 
-  T* get() {
-    if (!ptr_) {
-      ptr_.reset(init_());
-    }
+  T* get() const {
+    CheckInitialised();
     return ptr_.get();
   }
 
   typename std::add_lvalue_reference<T>::type operator*() const {
+    CheckInitialised();
     return *ptr_;
   }
 
-  T* operator->() const { return ptr_.get(); }
+  T* operator->() const { return get(); }
 
  private:
-  std::function<T*()> init_;
-  std::unique_ptr<T> ptr_;
+  void CheckInitialised() const {
+    if (!ptr_) {
+      ptr_.reset(init_());
+    }
+  }
+
+  const std::function<T*()> init_;
+  mutable std::unique_ptr<T> ptr_;
 };
+
+#endif  // LAZY_H