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copied!<blockquote> <p>I'm not sure this works either. It would seem I would have to define a validate function for each instance of a generic even if I'm not passing it in as a parameter.</p> </blockquote> <p>That is probably the <em>best</em> way to approach this; you're talking validation of data after all... and defaulting that could have unexpected behavior. (Any type that's crossing in/out of your system ought to be validated; e.g. File reads, DB reads, user-input, etc.)</p> <blockquote> <p>The point of having the default function in the generic was to eliminate duplicate code. Any other thoughts?</p> </blockquote> <p>Well, there is one method that springs to mind. It requires us to limit what we accept in our generic though. My other solutions are [almost] fully generalized and therefore would work on any non-limited type.</p> <p>Taking the attribute <code>'Valid</code> we see that the <a href="http://www.adaic.org/resources/add_content/standards/05aarm/html/AA-13-9-2.html" rel="nofollow">documentation</a> says this:<br> <code>The Valid attribute can be used to check the validity of data produced by unchecked conversion, input, interface to foreign languages, and the like.</code></p> <p>So we have a default validation, of sorts.<br> We also have a way to have attributes stand in for the default of function formal-parameters.<br> We have a way to default to visible functions.<br> Last we have nested generics.</p> <p>Now there's no generic formal type <code>scalar</code>, which would be useful here... but we have a way to limit the type of a formal parameter <code>Type T(<>) is (<>)</code> is limited to integral numerics, modular-types, and enumerations... all of which we know are scalar-types.</p> <pre><code>Generic Type Item(<>) is (<>); Package Generic_Base is -- To use this as a Ada-95 pkg delete everything after 'Boolean', -- create a body and return X'Valid from the implementation. Function Default_Validate(X : Item) Return Boolean is (X'Valid); Generic with function Validate(X:Item) return Boolean is Default_Validate; Package Generic_Nested is -- Operations requiring validation. End Generic_Nested; End Generic_Base; </code></pre> <p>Using these packages would be as follows:</p> <pre><code>Package Base is new Generic_Base( Integer ); Package Nested is new Base.Generic_Nested; </code></pre> <p>If you're happy in limiting the formal parameter to integrals/modulars/enumerations, this should work.</p> <p>So, there you go.</p> <hr> <p>Recommended reading: </p> <h2><a href="http://en.wikibooks.org/wiki/Ada_Programming/Generics#Generic_formal_types" rel="nofollow">Ada's Generic Formal Type System</a></h2> <hr> <p><sup>No syntax highlighting because it looks <strong><em>terrible</em></strong> on this.</sup></p>

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