Re: Invalid C++ or bug in GCC 4.8

From:
=?UTF-8?B?RGFuaWVsIEtyw7xnbGVy?= <daniel.kruegler@googlemail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Mon, 1 Jul 2013 05:58:33 -0700 (PDT)
Message-ID:
<kqro5s$2sa$1@dont-email.me>
On 2013-07-01 13:22, marcel.loose@googlemail.com wrote:

You cannot create an object of an abstract class type, so there
cannot be a function with such return type. The compiler error
message is completely reasonable here.


So, if I understand things correctly, the fix is easy. Instead of

      class ObjectFactory<Base (), TypeId> { };
      // ...
      typedef ObjectFactory< Abstract(), int> MyFactory;

I should write

      class ObjectFactory<Base* (), TypeId> { };
      // ...
      typedef ObjectFactory< Abstract* (), int> MyFactory;


Alternatively you could also write:

         class ObjectFactory<Base& (), TypeId> { };
         // ...
         typedef ObjectFactory< Abstract& (), int> MyFactory;

I always thought that the part between the angle brackets
represented the signature of the class' constructor, instead of the
return type.


In C++ the term "signature" has a very specific meaning, except for
function templates (or specializations thereof) it does *not* contain
the return type. Furthermore, there is no way to describe the type of
a constructor as a function type directly. Actually, constructors have
not a well-defined return type at all, the nearest approximation to
this would be a void return type.

In addition, your association of T() (for some type T) referring to a
constructor call is based on an *expression* T(), but in your example,
'Base()' and 'Abstract()' are not expressions, they are function
types.

HTH & Greetings from Bremen,

Daniel Kr?gler

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