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POC# Property Access vs Interface Implementation
 

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    <p>I'm writing a class to represent a <a href="http://www.getpivot.com" rel="nofollow noreferrer">Pivot</a> Collection, the root object recognized by Pivot. A Collection has several attributes, a list of facet categories (each represented by a <code>FacetCategory</code> object) and a list of items (each represented by a <code>PivotItem</code> object). Therefore, an extremely simplified Collection reads:</p> <pre><code>public class PivotCollection { private List&lt;FacetCategory&gt; categories; private List&lt;PivotItem&gt; items; // other attributes } </code></pre> <p>What I'm unsure of is how to properly grant access to those two lists. Because declaration order of both facet categories and items is visible to the user, I can't use sets, but the class also shouldn't allow duplicate categories or items. Furthermore, I'd like to make the Collection object as easy to use as possible. So my choices are:</p> <ol> <li><p>Have <code>PivotCollection</code> implement <code>IList&lt;PivotItem&gt;</code> and have accessor methods for <code>FacetCategory</code>: In this case, one would add an item to Collection <code>foo</code> by writing <code>foo.Add(bar)</code>. This works, but since a Collection is equally both kinds of list making it only pass as a list for one type (category or item) seems like a subpar solution.</p></li> <li><p>Create nested wrapper classes for <code>List</code> (<code>CategoryList</code> and <code>ItemList</code>). This has the advantage of making a consistent interface but the downside is that these properties would no longer be able to serve as lists (because I need to override the non-virtual <code>Add</code> method I have to implement <code>IList</code> rather than subclass <code>List</code>. Implicit casting wouldn't work because that would return the <code>Add</code> method to its normal behavior.</p></li> </ol> <p>Also, for reasons I can't figure out, <code>IList</code> is missing an <code>AddRange</code> method...</p> <pre><code>public class PivotCollection { private class CategoryList: IList&lt;FacetCategory&gt; { // ... } private readonly CategoryList categories = new CategoryList(); private readonly ItemList items = new ItemList(); public CategoryList FacetCategories { get { return categories; } set { categories.Clear(); categories.AddRange(value); } } public ItemList Items { get { return items; } set { items.Clear(); items.AddRange(value); } } } </code></pre> <p>Finally, the third option is to combine options one and two, so that <code>PivotCollection</code> implements <code>IList&lt;PivotItem&gt;</code> and has a property <code>FacetCategories</code>. </p> <p><strong>Question:</strong> Which of these three is most appropriate, and why?</p>
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    1. COYou should not make a class called `Collection`. Choose a more specific name.
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    2. COEdited to be `PivotCollection` - would that be better?
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    3. COSince it's not (directly) a collection of objects, it probably shouldn't end in `Collection`.
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