public override object Exec(NullType firstOperand, object arg)
{
// * Built-in types: no promotion, except string
if (this.secondOperand is BoolType || this.secondOperand is CharType || this.secondOperand is DoubleType || this.secondOperand is IntType || this.secondOperand is VoidType)
{
return(-1);
}
// * BCL Value Types (structs): No promotion
BCLClassType bclClass = TypeExpression.As <BCLClassType>(this.secondOperand);
if (bclClass != null)
{
if (bclClass.TypeInfo.IsValueType)
{
return(-1);
}
// * Correct promotion to classes that are not value types
return(0);
}
// * WriteType variable
TypeVariable typeVariable = this.secondOperand as TypeVariable;
if (typeVariable != null)
{
if (typeVariable.Substitution != null)
{
// * If the variable is bounded, the promotion is the one of its substitution
return(firstOperand.AcceptOperation(new PromotionLevelOperation(typeVariable.EquivalenceClass.Substitution), arg));
}
// * A free variable is complete promotion
return(0);
}
// * Union type
UnionType unionType = TypeExpression.As <UnionType>(this.secondOperand);
if (unionType != null)
{
return(unionType.SuperType(firstOperand));
}
// * Field type and bounded type variable
FieldType fieldType = TypeExpression.As <FieldType>(this.secondOperand);
if (fieldType != null)
{
return(firstOperand.AcceptOperation(new PromotionLevelOperation(fieldType.FieldTypeExpression), arg));
}
// * Correct Promotion
return(0);
}
