Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-pcd!hplsla!jima
From: jima@hplsla.HP.COM (Jim Adcock)
Newsgroups: comp.lang.c++
Subject: Re: coercion of x op= y verses x = x op y ???
Message-ID: <6590294@hplsla.HP.COM>
Date: 11 Oct 89 18:26:50 GMT
References: <6590279@hplsla.HP.COM>
Organization: HP Lake Stevens, WA
Lines: 31

// okay, okay -- the following "works" -- I don't know *why* I couldn't figure
// out how to do this earlier.  Unfortunately, now you can't explictely 
// coerce to (int), as may be "required" to send Int to a "C" routine like
// printf.  Instead you have to coerce to (int&) -- So now users have to
// remember if a class defines an (int) coercion or and (int&) coercion.
// [Its not practical to have both, since that results in mega-ambiguities]

// -- And no, I'm not really writing an "Int" class.  "Int" is just a 
// metaphor for writing C++ classes supporting "as-if" polymorphism.  For
// example, one might want to write an "IntStack" where the top-of-stack can
// be used "as-if" it were an int.

extern "C" {int printf(const char* const p, ...);};

class Int
{
  private: int i;
  public:  
    Int(int I=0):i(I){}
    operator int&(){return i;}
};

void main()
{
  Int I=10;
  printf("%d\n",(int&)I);
  I = I * I;			// okay by both g++ 1.5.x and AT&T 2.0
  printf("%d\n",(int&)I);
  I *= I; 			// g++ 1.35.x accepts, 2.0 accepts it too
  printf("%d\n",(int&)I);
}