public void BinaryOperatorOverloadResolution(BinaryOperatorKind kind, BoundExpression left, BoundExpression right, BinaryOperatorOverloadResolutionResult result)
{
Debug.Assert(left != null);
Debug.Assert(right != null);
Debug.Assert(result.Results.Count == 0);
// We can do a table lookup for well-known problems in overload resolution.
BinaryOperatorEasyOut(kind, left, right, result);
if (result.Results.Count > 0)
{
return;
}
// The following is a slight rewording of the specification to emphasize that not all
// operands of a binary operation need to have a type.
// SPEC: An operation of the form x op y, where op is an overloadable binary operator is processed as follows:
// SPEC: The set of candidate user-defined operators provided by the types (if any) of x and y for the
// SPEC operation operator op(x, y) is determined.
GetUserDefinedOperators(kind, left, right, result.Results);
// SPEC: If the set of candidate user-defined operators is not empty, then this becomes the set of candidate
// SPEC: operators for the operation. Otherwise, the predefined binary operator op implementations, including
// SPEC: their lifted forms, become the set of candidate operators for the operation.
if (!result.AnyValid())
{
GetAllBuiltInOperators(kind, left, right, result.Results);
}
// SPEC: The overload resolution rules of 7.5.3 are applied to the set of candidate operators to select the best
// SPEC: operator with respect to the argument list (x, y), and this operator becomes the result of the overload
// SPEC: resolution process. If overload resolution fails to select a single best operator, a binding-time
// SPEC: error occurs.
BinaryOperatorOverloadResolution(left, right, result);
}
private void BinaryOperatorEasyOut(BinaryOperatorKind kind, BoundExpression left, BoundExpression right, BinaryOperatorOverloadResolutionResult result)
{
var leftType = left.Type;
if (leftType == null)
{
return;
}
var rightType = right.Type;
if (rightType == null)
{
return;
}
if (PossiblyUnusualConstantOperation(left, right))
{
return;
}
var easyOut = BinopEasyOut.OpKind(kind, leftType, rightType);
if (easyOut == BinaryOperatorKind.Error)
{
return;
}
BinaryOperatorSignature signature = this.Compilation.builtInOperators.GetSignature(easyOut);
Conversion? leftConversion = Conversions.FastClassifyConversion(left.Type, signature.LeftType);
Conversion? rightConversion = Conversions.FastClassifyConversion(right.Type, signature.RightType);
Debug.Assert(leftConversion.HasValue && leftConversion.Value.IsImplicit);
Debug.Assert(rightConversion.HasValue && rightConversion.Value.IsImplicit);
result.Results.Add(BinaryOperatorAnalysisResult.Applicable(signature, leftConversion.Value, rightConversion.Value));
}
// Takes a list of candidates and mutates the list to throw out the ones that are worse than
// another applicable candidate.
private void BinaryOperatorOverloadResolution(
BoundExpression left,
BoundExpression right,
BinaryOperatorOverloadResolutionResult result
)
{
// SPEC: Given the set of applicable candidate function members, the best function member in that set is located.
// SPEC: If the set contains only one function member, then that function member is the best function member.
if (result.GetValidCount() == 1)
{
return;
}
// SPEC: Otherwise, the best function member is the one function member that is better than all other function
// SPEC: members with respect to the given argument list, provided that each function member is compared to all
// SPEC: other function members using the rules in 7.5.3.2. If there is not exactly one function member that is
// SPEC: better than all other function members, then the function member invocation is ambiguous and a binding-time
// SPEC: error occurs.
// UNDONE: This is a naive quadratic algorithm; there is a linear algorithm that works. Consider using it.
var candidates = result.Results;
for (int i = 0; i < candidates.Count; ++i)
{
if (candidates[i].Kind != OperatorAnalysisResultKind.Applicable)
{
continue;
}
// Is this applicable operator better than every other applicable method?
for (int j = 0; j < candidates.Count; ++j)
{
if (i == j)
{
continue;
}
if (candidates[j].Kind == OperatorAnalysisResultKind.Inapplicable)
{
continue;
}
var better = BetterOperator(candidates[i].Signature, candidates[j].Signature, left, right);
if (better == BetterResult.Left)
{
candidates[j] = candidates[j].Worse();
}
else if (better == BetterResult.Right)
{
candidates[i] = candidates[i].Worse();
}
}
}
}
