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    <blockquote> <p>So, not only must the general specialization not conflict with the array specialization, it can't conflict with any specialization that names a user-defined type. That is, if the user declares a specialization, the existence of the general argument getter cannot affect whether it's chosen.</p> </blockquote> <p>I don't understand this. What do you mean?</p> <hr> <blockquote> <p>Is it OK for the implementation to expose a general template indexer through std::tuple_element?</p> </blockquote> <p>It's impossible to do so for the general case. Imagine this one</p> <pre><code>template&lt;int A, char B, long C, class D, int &amp;X, int(*Handler)()&gt; struct funny_template { }; int x, y(); std::tuple_element&lt;3, funny_template&lt;1, 2, 3, long, x, y&gt; &gt;::type along = 0; </code></pre> <p>Happy macro meta-programming :)</p> <hr> <blockquote> <p>I haven't made many forays into the partial ordering rules. Is this analysis correct?</p> </blockquote> <p>Partial ordering for two partial specializations</p> <pre><code>template&lt;class A1, ..., class AN&gt; class T&lt;Am1, ..., AmM&gt;; template&lt;class B1, ..., class BL&gt; class T&lt;Bm1, ..., BmM&gt;; </code></pre> <p>Works like transforming them to function templates and ordering <em>them</em></p> <pre><code>template&lt;class A1, ..., class AN&gt; void f(T1&lt;Am1, ..., AmM&gt;); template&lt;class B1, ..., class BL&gt; void f(T2&lt;Bm1, ..., BmM&gt;); </code></pre> <p>Partial ordering like your analysis says correctly puts unique types for each template parameter transforming it to an argument for argument deduction, comparing it to the other template</p> <pre><code>T1A&lt;Uam1, ..., UAmM&gt; -&gt; T2&lt;Bm1, ..., BmM&gt; T2A&lt;UBm1, ..., UBmM&gt; -&gt; T1&lt;Am1, ..., AmM&gt; </code></pre> <p>If there is a non-deduced context it's not compared like usual. Like if <code>BmM</code> is <code>typename Foo::X</code>, the first deduction above would consider deduction of the last sub-type as success because there can't be a mismatch for a nondeduced context. The other way around though, <code>Foo::X</code> against <code>AmM</code> <em>can</em> mismatch though if <code>AmM</code> is not a nondeduced context itself. </p> <p>If deduction succeeds for one round and not the other way around (... leaving off some other rules because they only happen for real function template ordering), the template on the right side above for the round that failed deduction is more specialized. Otherwise, the partial specializations are unordered. </p>
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    1. POMay std::tuple_element double as a universal template argument retriever?
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    1. USJohannes Schaub - litb
    1. USJohannes Schaub - litb
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    1. POMay std::tuple_element double as a universal template argument retriever?
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    1. COThe quote you pasted is just setting up the question. An implementation is nonconforming if it breaks a user specialization. Conversely, if it never interferes, I believe this feature would conform.
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    2. COJust using the term "general template indexer" to refer to the thing which *can* exist ;v) … So, it will always be ordered after a user specialization, or not? Is there a valid user specialization which only mentions their type in a non-deduced context? If so, would it "depend on a user-defined type" per 17.6.3.2.1/1? Or does that term need to be clarified?
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    3. CO(Conclusion: A template which mentions user classes only in non-deduced contexts does not depend on a user-defined type.)
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