Re: class conditional initialization question

From:
SG <s.gesemann@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Fri, 24 Sep 2010 01:02:22 -0700 (PDT)
Message-ID:
<af692e9d-81b3-45cf-a838-db7c038ca978@z25g2000vbn.googlegroups.com>
On 24 Sep., 00:27, zl2k wrote:

I have

  class Foo{


    public:

    explicit Foo(int a);
    explicit Foo(int a, int b);
  }

how can I conditionally create an instance of Foo not using the
pointer?

I want something like

  Foo foo; // it's already initialized, do I need a dummy explicit Foo()
  in the Foo class?
  if (use1var){
    // initialize foo with 1 variable, how?}
  else{
    // initialize foo with 2 variable}


    }

  // play with foo

I can put //play with foo within the if else, but that will make the
code too bulky.


You could write:

   Foo foo = use1var ? function1() : function2();
   // play with foo

where function1 and function2 return a Foo object by value.
Or, you could write:

   boost::scoped_ptr<Foo> pfoo;
   if (use1var) {
      pfoo.reset( new Foo(23,42) );
   } else {
      pfoo.reset( new Foo(1729) );
   }
   // play with *pfoo

Or, you could write:

   boost::optional<Foo> ofoo = boost::none;
   if (use1var) {
      ofoo = Foo(23,42); // "copy initialization"
   } else {
      ofoo = Foo(1729); // "copy initialization"
   }
   // play with *ofoo

Unfortunately boost::optional doesn't seem to allow an in-place
construction. At least I don't see anything to that effect in the
documentation.

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