Template Return Type with Default Value

Question

So in writing a C++ template class, I have defined a method that returns an object of the templated type, as such:

template 
class Foo
{
public         


        

Answer 1

The line

T t;

Default constructs objects, yet declares uninitialized built-in types. There is no syntax to 'default construct' a local variable.

Therefore it's not trivial to write generic code that initializes a variable, whether built-in or class.

Wrapping the type into a member variable, however, may present a workaround that does not need copy construction (apart from the return statement):

template< typename T > struct Initializer {
   T t;
   Initializer()
   :t() // ====> default construction, works for classes _and_ built-in
   {}
};

Using this wrapper, you can build your code in a generic way:

template T foo() {
  Initializer i;
  // fill in i.t to your liking
  return i.t;
}

See a full-blown snippet at codepad.