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    <p>One possibly quite easy way of achieving this is to provide a method that takes a function to retrieve the item to compare. Something like:</p> <pre><code>private List&lt;T&gt; Reduce&lt;T, TProp&gt;(List&lt;T&gt; list, Func&lt;T, TProp&gt; getId) { } </code></pre> <p><sub>I have deliberately not provided an implementation for <code>Reduce</code> because I cannot head-compile the dependencies of things like <code>Contains</code>, which often need items that implement interfaces.</sub></p> <p>This will allow you to supply different classes and use the <code>Func</code> to generalise the retrieval of the ID:</p> <pre><code>var customers = new List&lt;Customer&gt;(); customers = Reduce&lt;Customer, Guid&gt;(customers, c =&gt; c.CustomerId); var products = new List&lt;Product&gt;(); products = Reduce&lt;Product, int&gt;(products, p =&gt; p.ProductId); </code></pre> <p>The support for type inference in the compiler will often let you get away with just:</p> <pre><code>customers = Reduce(customers, c =&gt; c.CustomerId); products = Reduce(products, p =&gt; p.ProductId); </code></pre> <p>You may have to constrain <code>TProp</code> with <code>IEquatable</code> or something in order to get it to work with a <code>Contains</code> implementation, but this is the route I would explore first:</p> <pre><code>private List&lt;T&gt; Reduce&lt;T, TProp&gt;(...) where TProp : IEquatable&lt;TProp&gt; </code></pre> <p><hr/> An alternative is to generalise the functionality over the classes using an interface that exposes the ID. In the face of <code>Func</code> I now tend to err away from this route if I am making the changes retroactively.</p>
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    1. POHow to make a method work for Lists of different objects?
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    1. USAdam Houldsworth
    1. USAdam Houldsworth
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    1. COthis concept looks quiet interesting, but how could i look inside the properties inside getId?
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      1. USRaymond Osterbrink
    2. CO@RaymondOsterbrink You use `getId` as a method and call it to get the physical Id value: `var theId = getId(o);`
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      1. USAdam Houldsworth
    3. COyou mean like: foreach(object o in list) {var theId = getId(o);} ? this does not work.
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      1. USRaymond Osterbrink
 

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