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copied!<p><code>Lazy<T></code> (<a href="http://msdn.microsoft.com/en-us/library/dd642331.aspx">MSDN</a>) is a generic wrapper which allows creating an instance of <code>T</code> on demand by holding a <code>T</code> factory method (<code>Func<T></code>) and calling it when <code>Vaue</code> property getter is accessed. </p> <p><code>LazyInitializer</code> - static class with a set of static methods, this is just a helper which uses <a href="http://msdn.microsoft.com/en-us/library/system.activator.createinstance.aspx">Activator.CreateInstance()</a> (reflection) able to instantiate a given type instance. It does not keep any local private fields and does not expose any properties, so no memory usage overheads. </p> <p>Worth noting that both classes uses <code>Func<T></code> as instance factory.</p> <p><a href="http://msdn.microsoft.com/en-us/library/system.threading.lazyinitializer.aspx">MSDN</a> says in few words about <code>LazyInitializer</code> class:</p> <blockquote> <p>These routines avoid needing to allocate a dedicated, lazy-initialization instance, instead using references to ensure targets have been initialized as they are accessed.</p> </blockquote> <p>PS: I found interesting a way how <code>LazyIntiializer</code> checks whether instance already initialized, it just compare a passed in reference to a <code>default(T)</code>, nice:</p> <pre><code>private static T EnsureInitializedCore<T>(ref T target, Func<T> valueFactory) where T : class { T t = valueFactory(); if (t == null) { throw new InvalidOperationException(Environment.GetResourceString("Lazy_StaticInit_InvalidOperation")); } Interlocked.CompareExchange<T>(ref target, t, default(T)); return target; } </code></pre> <p>What seems strange to me, it creates a new instance each time before an actual check:</p> <pre><code>T t = valueFactory(); // ... and only then does check </code></pre>

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