Databases
StackOverflow2013
Postsdbo
POOptionally supporting initializer_list construction for templates maybe wrapping containers
Body
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POOptionally supporting initializer_list construction for templates maybe wrapping containers
    text
    copied!<p>If I have a template that wraps a standard container, it seems I can reasonably easily delegate the initializer_list constructor:</p> <pre><code>template&lt;typename T&gt; struct holder { T t_; holder() : t_() {} holder(std::initializer_list&lt;typename T::value_type&gt; values) : t_(values) {} }; </code></pre> <p>So this works nicely with std::vector, for instance.</p> <pre><code>int main(int argc, char* argv[]) { holder&lt;std::vector&lt;int&gt;&gt; y{1,2,3}; return EXIT_SUCCESS; } </code></pre> <p>But it pretty obviously doesn't work for T as 'int', or any other type that doesn't have a nested value_type typedef. So, I'd like to use some sort of enable_if or similar trick to make the initializer_list constructor not be emitted unless T both defines a nested value_type typedef, and is constructible from std::initializer_list.</p> <p>I tried the following, but it still doesn't work, because the compiler (clang++ 3.1 in my case), still trips over the invalid T::value_type when T is int:</p> <pre><code>holder(typename std::enable_if&lt;std::is_constructible&lt;T, std::initializer_list&lt;typename T::value_type&gt;&gt;::value, std::initializer_list&lt;typename T::value_type&gt;&gt;::type values) : t_(values) {} </code></pre> <p>Any thoughts on how to express the concept "give this template on T an initializer list constructor over T's value_type, if and only if T has a value_type typedef and is constructible from an initializer_list of T::value_type".</p>
 

Querying!

 
Guidance
An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload