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POType aliases for Java generics
 

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    <p>I have a fairly complicated set of generic classes in Java. For example, I have an interface</p> <pre><code>interface Doable&lt;X,Y&gt; { X doIt(Y y); } </code></pre> <p>and the implementation</p> <pre><code>class DoableImpl implements Doable&lt;Foo&lt;Bar&lt;Baz,Qux&gt;&gt;,Foo&lt;Bar&lt;Zot,Qux&gt;&gt;&gt; { Foo&lt;Bar&lt;Baz,Qux&gt;&gt; doIt(Foo&lt;Bar&lt;Zot,Qux&gt;&gt; fooBZQ) { ... } } </code></pre> <p>In the real implementation, <code>Doable</code> has quite a few methods and so <code>Foo&lt;Bar&lt;Baz,Qux&gt;&gt;</code>, etc., appear over and over again. (Believe it or not, the generic types are quite a bit more painful than this. I've simplified them for the example.)</p> <p>I'd like to simplify these, to save myself typing and to ease the strain on my eyes. What I'd like is to have a simple "type alias" for <code>Foo&lt;Bar&lt;Baz,Qux&gt;&gt;</code>, etc., say <code>FooBBQ</code> and <code>FooBZQ</code>. </p> <p>My current idea is to define wrapper classes:</p> <pre><code>class FooBBQ { public static FooBBQ valueOf(Foo&lt;Bar&lt;Baz,Qux&gt;&gt; fooBBQ) { return new FooBBQ(fooBBQ); } private Foo&lt;Bar&lt;Baz,Qux&gt;&gt; fooBBQ; private FooBBQ(Foo&lt;Bar&lt;Baz,Qux&gt;&gt; fooBBQ) { this.fooBBQ = fooBBQ; } public Foo&lt;Bar&lt;Baz,Qux&gt;&gt; toGeneric() { return fooBBQ; } } class FooBZQ { /* pretty much the same... */ } class DoableImpl implements Doable&lt;FooBBQ,FooBZQ&gt; { FooBBQ doIt(FooBZQ fooBZQ) { ... } } </code></pre> <p>This works well, but it has a few drawbacks:</p> <ol> <li>We need to define separate wrappers for each generic instance. The wrapper classes are short and stylized, but I can't figure out a way to macro-ize them. </li> <li><p>We have the translation overhead (conceptually, if not operationally) of calling <code>valueOf</code> and <code>toGeneric</code> to convert between <code>FooBBQ</code> and <code>Foo&lt;Bar&lt;Baz,Qux&gt;&gt;</code>. For example, if <code>doIt</code> calls into some library routine that expects a <code>Foo&lt;Bar&lt;Zot,Qux&gt;&gt;</code> (which the real implementation does), we end up with something like</p> <pre><code>return FooBBQ.valueOf( libraryCall( fooBZQ.toGeneric() ) ) </code></pre> <p>where we would originally have had</p> <pre><code>return libraryCall(fooBZQ); </code></pre></li> </ol> <p>Is there some other way to get the "type alias" behavior I want here? Perhaps using some third-party macro toolset? Or do I need to accept that I'm going to have to do a lot of typing, one way (using the generic types in the implementation) or the other (writing wrappers for them)? Maybe having this many generic parameters flying around is just a bad idea and I need to re-think the problem?</p> <p>[UPDATE] OK, I'm banning any further "don't do that" answers. Take it as a given that <code>Foo&lt;Bar&lt;Baz,Qux&gt;&gt;</code> has genuine value in my problem domain (Pete Kirkham may be right that it has <em>enough</em> value to get a proper wrapper class with a descriptive name). But this is a programming problem; don't try to define the problem away.</p>
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    1. USChris Conway
    1. USChris Conway
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      1. USNick Klauer
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    1. COI'm going to say 'probably yes' to the last one, but don't really have any constructive feedback :P It looks like a mess! Good luck!
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      1. USAndy Mikula
    2. COI think this question would make a good proposal for Java. If you could propose a Type Aliasing feature to Oracle, I think it would be a great language feature that will simplify the language and make the source code more readable.
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      1. USBasil Musa
    3. COKnee deep in Java today and wanted to clean up some verbose code...not only do I not get type inference, but no type aliasing either. *sob*
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      1. USKent Boogaart
 

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