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POreturn generic type from generic function
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  1. POreturn generic type from generic function
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    copied!<p>we have a method more or less like the following. however we currently return List which in function bla() would return <code>List&lt;Bar&gt;</code> at runtime.</p> <p>I'm looking for a way to make both</p> <pre><code>List&lt;Interface&gt; = troubleFuction(foo, bar.getCLass());; </code></pre> <p>and</p> <pre><code>List&lt;Bar&gt; = troubleFuction(foo, bar.getCLass());; </code></pre> <p>possible. basicaly i want it to return List which would be compatible with interface however this gives the following error</p> <p>*Type mismatch: cannot convert from <code>List&lt;capture#3-of ? extends Bar&gt;</code> to <code>List&lt;Interface&gt;*</code> </p> <p>is there any way to make this return type possible or does runtime erasure make this impossible</p> <pre><code>public &lt;T1 extends Interface, T2 extends Interface&gt; List&lt;"problem"&gt; troubleFunction( T1 in, Class&lt;T2&gt; clazz) { return in.doStuffWhichGeneratesAlistOF(clazz) } public void bla() { Foo foo = new Foo(); // implements interface Bar bar = new Bar(); // implements interface List&lt;Interface&gt; ifaces = toubleFuction(foo, bar.getCLass()); List&lt;Bar&gt; mustAlsoWork = toubleFuction(foo, bar.getCLass()); } </code></pre> <p>edit: in a lot of the existing code base the method is called like</p> <pre><code>List&lt;Bar&gt; result = troubleFunction(List&lt;Interface&gt; list, Bar.class); </code></pre> <p>thus this return type must stay compatible (rewrite/re-factor is not an option)</p> <p>essentially i want the method to return List<code>&lt;? super Bar&gt;</code> if called as</p> <pre><code>troublefunction(foo, Bar.class); </code></pre> <p>and <code>List&lt;? super Foo&gt;</code> when called as</p> <pre><code>troublefunction(foo, Bar.class); </code></pre>
 

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