Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>This works, though is somewhat nasty:</p> <pre><code>#include &lt;string&gt; #include &lt;iostream&gt; class A { public: std::string msg; A(std::string s) { msg = s;} void filter() { std::cout &lt;&lt; "Message A = " &lt;&lt; msg &lt;&lt; std::endl;} }; class B { public: std::string msg; B(std::string s) { msg = s;} void filter() { std::cout &lt;&lt; "The B message: " &lt;&lt; msg &lt;&lt; std::endl;} }; // ------------- class Base { public: virtual void filter() = 0; virtual ~Base() {} }; template&lt;class C&gt; class Wrapper: public Base { public: Wrapper( C * impl ): m_impl(impl) { } ~Wrapper() { delete m_impl; } virtual void filter() { m_impl-&gt;filter(); } private: C * m_impl; }; // ------------- int main() { Base * f = NULL; int type = 1; switch (type) { case 1: f = new Wrapper&lt;A&gt;(new A("hi from A")); break; case 2: f = new Wrapper&lt;B&gt;(new B("hello from B")); break; } f-&gt;filter(); delete f; } </code></pre> <hr> <p>And the C++11, exception-safe variant with perfect forwarding of the constructors. Just <code>Wrapper</code> and <code>main()</code> are different from above, here they are:</p> <pre><code>template&lt;typename T&gt; class Wrapper : public Base { public: template&lt;typename... Args&gt; Wrapper(Args&amp;&amp;... args) : m_impl(std::forward&lt;Args&gt;(args)...) {} virtual void filter() { m_impl.filter(); } private: T m_impl; }; // ------------- int main() { std::unique_ptr&lt;Base&gt; f; int type = 1; switch (type) { case 1: f.reset(new Wrapper&lt;A&gt;("hi from A")); break; case 2: f.reset(new Wrapper&lt;B&gt;("hello from B")); break; } f-&gt;filter(); } </code></pre>
    singulars
    1. This table or related slice is empty.
    1. POC++ How to call common method from classes without a shared superclass?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USsyam
    1. USmoonshadow
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COThat's actually not that nasty...
      singulars
      1. PO
      1. USNik Bougalis
    2. COA less nasty approach would involve C, not C*, being a member of Wrapper, with specialisations to provide constructors where they differ. The set of declarations would get more verbose, but it'll be much nicer at the point of use and have one less level of indirection. It's ten to midnight here though so I'll leave that to someone else :)
      singulars
      1. PO
      1. USmoonshadow
    3. CO`deleting object of abstract class type ‘Base’ which has non-virtual destructor will cause undefined behaviour`. Also, smart pointers instead of naked pointers, this is extremely brittle as it is.
      singulars
      1. PO
      1. USsyam
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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