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POUnderstanding a change to protected/base member usage in F# 3.0
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  1. POUnderstanding a change to protected/base member usage in F# 3.0
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    copied!<p>F# 3.0 adds stricter checks for calls to <code>base</code> and <code>protected</code> members. I have something like the following abstract class in C# that has <code>protected static</code> helper methods to be used by derived classes.</p> <pre class="lang-cs prettyprint-override"><code>public abstract class Processor { public abstract void Process(); protected static void Helper(object arg) { } } </code></pre> <p>In F#, one of those helper methods is passed as a first-class function:</p> <pre class="lang-ml prettyprint-override"><code>type DerivedProcessor() = inherit Processor() let init f = f () override x.Process() = init Processor.Helper </code></pre> <p>It compiles without complaint in 2.0, but in 3.0 produces an error:</p> <blockquote> <p>A protected member is called or 'base' is being used. This is only allowed in the direct implementation of members since they could escape their object scope.</p> </blockquote> <p>OK, it's easy enough to comply, just wrap the call in another static member </p> <pre class="lang-ml prettyprint-override"><code>static member private HelperWrapper(arg) = Processor.Helper(arg) </code></pre> <p>and pass that intead. But why?</p> <p>C# has no problem with this same pattern.</p> <pre class="lang-cs prettyprint-override"><code>public class HappyToCompile : Processor { private void Init(Action&lt;object&gt; f) { f(null); } public override void Process() { Init(Helper); } } </code></pre> <p><strong>The questions:</strong></p> <ol> <li>Why were the stricter checks added?</li> <li>(and related) What terrible problem does such a trivial workaround address?</li> <li>Is there a better design that this is supposed to encourage?</li> </ol>
 

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