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Fallible.h

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//=================================================
//
//
//
// Copier: Peter Sherwood
// See Barton+Nackman p 158
//
//
//===================================================
#ifndef ATLFAST_FALLIBLE_H
#define ATLFAST_FALLIBLE_H
#include<string>

namespace Atlfast{
  class InvalidStateErr{
  public:
    InvalidStateErr(){}
    InvalidStateErr(::std::string s): m_string(s){}
    void print(){cout<<m_string<<endl;}
  private:
    std::string m_string;
  };

  template<class T> class Fallible {
  public:
    Fallible(const T& t):is_valid(true), instance(t){}   //instance exists
    Fallible():is_valid(false){}                 //instance does not exist
    bool failed() const{ return !is_valid;}      //return true is no instance
    bool valid()  const{ return is_valid;}       //return true instance exists
    void invalidate()  { is_valid = false;}      //set invalid
    //    operator T() const{
    //  if(failed()) {::std::string s("Invalid State"); throw s;}             
    //  return instance;
    //}                                             //conversion to instance type
    operator T() const{
      if(failed()) {
        ::std::string s("Fallible in Invalid State");
        //      throw InvalidStateErr(s);
        //      throw InvalidStateErr(s);
        throw InvalidStateErr();
      }             
      return instance;
    }                                             //conversion to instance type
  private:
    bool is_valid;
    T instance;
  };
    
}
#endif

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