14.52.txt

Exercise 14.52: Which operator+, if any, is selected for each of the addition
expressions? List the candidate functions, the viable functions, and the type
conversions on the arguments for each viable function:

	struct LongDouble {
		// member operator+ for illustration purposes; + is usually a nonmember
		LongDouble operator+(const SmallInt&);
		// other members as in § 14.9.2 (p. 587)
	};
	LongDouble operator+(LongDouble&, double);
	SmallInt si;
	LongDouble ld;
	ld = si + ld;
	ld = ld + si;

By Faisal Saadatmand

	ld  = si + ld;

The call is ambiguous.

Candidate functions: (step 1)
LongDouble operator+(LongDouble&, double)
LongDouble::operator+(const SmallInt&)
SmallInt Operator+(const SmallInt &, const SmallInt &)
built-in operator+ versions

Viable functions: (step 2)
All but the built-in operator+ versions are not viable. The first two
user-defined operator+ are excluded because the left-hand side operand (si) is
of type SmallInt, which does not match the left-hand parameter type of the
defined functions. The third function is excluded too because, though the
left-hand parameter is SmallInt, there is no defined conversion function for
LongDouble to SmallInt in either classes to convert ld that would cause a match
with the right-hand side parameter. 

Type conversions (arguments): (step 3)
With the built-in operator+ we have two possibilities:
a) convert si to int and ld to double to use built-in operator+(int, double)
b) convert si to in and ld to double to use the built-in operator+(int, float)

	
	ld = ld + si;

The call uses LongDouble::operator+(const SmallInt&)

Candidate functions: (step 1)
LongDouble operator+(LongDouble&, double)
LongDouble::operator+(const SmallInt&)
SmallInt Operator+(const SmallInt &, const SmallInt &)
built-in operator+ versions

Viable functions: (step 2)
LongDouble operator+(LongDouble&, double) // rhs operand matches rhs parameter
LongDouble::operator+(const SmallInt&)    // same as above
built-in operator+ versions  // arguments are convertible to arithmetic types

Type conversion: (step 3)
LongDouble::operator+(const SmallInt&) is an exact match.

 For explanations on function matching in general and overloaded operator and
 function matching especially refer to pages 242 to 246 and 587 to 588.