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POGeneric base class wraps nested generic class to reduce type argument specification: Is there a name for this pattern?
 

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  1. POGeneric base class wraps nested generic class to reduce type argument specification: Is there a name for this pattern?
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    <p>Ok question title is far from being self-explanatory. I see myself doing this often:</p> <p>From <a href="https://stackoverflow.com/questions/98033/wrap-a-delegate-in-an-iequalitycomparer">this answer</a>:</p> <pre><code>public static class Equality&lt;T&gt; { public static IEqualityComparer&lt;T&gt; CreateComparer&lt;K&gt;(Func&lt;T, K&gt; keySelector) { return new KeyEqualityComparer&lt;K&gt;(keySelector); } class KeyEqualityComparer&lt;K&gt; : IEqualityComparer&lt;T&gt; { readonly Func&lt;T, K&gt; keySelector; public KeyEqualityComparer(Func&lt;T, K&gt; keySelector) { this.keySelector = keySelector; } public bool Equals(T x, T y) { ---- } public int GetHashCode(T obj) { .... } } } </code></pre> <p>What did I do: There is an implementation detail <code>KeyEqualityComparer&lt;T, K&gt;</code> which I had to call: </p> <pre><code>new KeyEqualityComparer&lt;Person, int&gt;(p =&gt; p.ID); </code></pre> <p>By nesting it as a private class, not only did I hide the implementation (the public constructor of internal class is obscure now), but got a better syntax:</p> <pre><code>Equality&lt;Person&gt;.CreateComparer(p =&gt; p.ID); </code></pre> <p>Note here that I haven't inherited nested class from the parent class (which is static). </p> <p>Or sometimes I see myself <a href="https://codereview.stackexchange.com/questions/25131/generic-wrapper-for-equality-and-hash-implementation-is-there-a-way-i-can-make">doing this</a>:</p> <pre><code>public abstract class Equater&lt;T&gt; : IEqualityComparer&lt;T&gt; { public static Equater&lt;T&gt; Create&lt;TKey&gt;(Func&lt;T, TKey&gt; keySelector) { return new Impl&lt;TKey&gt;(keySelector); } public abstract bool Equals(T x, T y); public abstract int GetHashCode(T obj); class Impl&lt;TKey&gt; : Equater&lt;T&gt; { readonly Func&lt;T, TKey&gt; keySelector; public Impl(Func&lt;T, TKey&gt; keySelector) { this.keySelector = keySelector; } public override bool Equals(T x, T y) { ---- } public override int GetHashCode(T obj) { .... } } } </code></pre> <p>Another similar one <a href="https://stackoverflow.com/a/16082916/661933">here</a></p> <pre><code>public class Accessor&lt;S&gt; { public static Accessor&lt;S, T&gt; Create&lt;T&gt;(Expression&lt;Func&lt;S, T&gt;&gt; memberSelector) { return new GetterSetter&lt;T&gt;(memberSelector); } class GetterSetter&lt;T&gt; : Accessor&lt;S, T&gt; { public GetterSetter(Expression&lt;Func&lt;S, T&gt;&gt; memberSelector) : base(memberSelector) { } } } public class Accessor&lt;S, T&gt; : Accessor&lt;S&gt; { Func&lt;S, T&gt; Getter; Action&lt;S, T&gt; Setter; public bool IsReadable { get; private set; } public bool IsWritable { get; private set; } public T this[S instance] { get { if (!IsReadable) throw new ArgumentException("Property get method not found."); return Getter(instance); } set { if (!IsWritable) throw new ArgumentException("Property set method not found."); Setter(instance, value); } } protected Accessor(Expression&lt;Func&lt;S, T&gt;&gt; memberSelector) //access not given to outside world { ---- } } </code></pre> <p>Note that in these two cases I inherited from wrapping class. So now not only did I get the benefits of the former but I can also maintain a list like this:</p> <pre><code>List&lt;Equater&lt;Person&gt;&gt; { persons with different implementations }; </code></pre> <p>Its helping me from time to time. <strong>So I'm curious to know if there is a name for this pattern?</strong></p>
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