HOWTO use a Factory

 Goran <>
Wed, 22 Aug 2007 14:36:17 -0700
Hi all,

i have some questions/problems about "Factories".

My origin is a constructor which needs a string in special format.

An example:

class Example_t {

                Example_t(std::string &aString);

My first idea was to check "aString" IN the constructor with
"boost::regex" AND to throw an exception if "aString" was bad.

Now I know it's bad to throw an exception in a constructor.

But what else?

How can I AVOID elegant a construction of an instance of "Example_t"
if "aString" is in bad format?

I've read a lot at the net but I'm still unhappy. At some other forum
I got the information to use something like that:

class Validator
  virtual bool validate(std::string) = 0;

class A

class Factory
  static A createA(std::string, *Validator);
  static B createB(std::string, *Validator);

But I don't understand how to AVOID a construction with classes above
if the string is in bad format?



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