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    <p>Actually, things got much easier in C++11 thanks to the <code>decltype</code> and late return bindings machinery.</p> <p>Now, it's just simpler to use methods to test this:</p> <pre><code>// Culled by SFINAE if reserve does not exist or is not accessible template &lt;typename T&gt; constexpr auto has_reserve_method(T&amp; t) -&gt; decltype(t.reserve(0), bool()) { return true; } // Used as fallback when SFINAE culls the template method constexpr bool has_reserve_method(...) { return false; } </code></pre> <p>You can then use this in a class for example:</p> <pre><code>template &lt;typename T, bool b&gt; struct Reserver { static void apply(T&amp; t, size_t n) { t.reserve(n); } }; template &lt;typename T&gt; struct Reserver &lt;T, false&gt; { static void apply(T&amp; t, size_t n) {} }; </code></pre> <p>And you use it so:</p> <pre><code>template &lt;typename T&gt; bool reserve(T&amp; t, size_t n) { Reserver&lt;T, has_reserve_method(t)&gt;::apply(t, n); return has_reserve_method(t); } </code></pre> <p>Or you can choose a <code>enable_if</code> method:</p> <pre><code>template &lt;typename T&gt; auto reserve(T&amp; t, size_t n) -&gt; typename std::enable_if&lt;has_reserve_method(t), bool&gt;::type { t.reserve(n); return true; } template &lt;typename T&gt; auto reserve(T&amp; t, size_t n) -&gt; typename std::enable_if&lt;not has_reserve_method(t), bool&gt;::type { return false; } </code></pre> <p>Note that this switching things is actually not so easy. In general, it's much easier when just SFINAE exist -- and you just want to <code>enable_if</code> one method and not provide any fallback:</p> <pre><code>template &lt;typename T&gt; auto reserve(T&amp; t, size_t n) -&gt; decltype(t.reserve(n), void()) { t.reserve(n); } </code></pre> <p>If substitution fails, this method is removed from the list of possible overloads.</p> <p><em>Note: thanks to the semantics of <code>,</code> (the comma operator) you can chain multiple expressions in <code>decltype</code> and only the last actually decides the type. Handy to check multiple operations.</em></p>
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    1. USMatthieu M.
    1. USMatthieu M.
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    1. CODoesn't `T` need to be a literal type in order to be a parameter to a `constexpr` function? Ok, on templates, the `constexpr` is dropped at instantiation time when it can't be `constexpr`, but you're using it in a template argument list, where it has to be.
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      1. USMarc Mutz - mmutz
    2. CO@Marc: No, you got nearly no restrictions on what can be a parameter.
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    3. COOk, this gave me the right direction. After successive simplifications, I got it to work requiring minimal C++11 support (just `decltype`) by keeping the structure of the 2nd C++98 version, but replacing the `Yes` versions with a single `template <typename T> static decltype(static_cast<const T*>(0)->isNull(),Yes()) check(int);` one.
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