//
// 7.9.6 Reference type equality operators
//
Binary ResolveOperatorEqualityRerefence (ResolveContext ec, Type l, Type r)
{
//
// operator != (object a, object b)
// operator == (object a, object b)
//
// TODO: this method is almost equivalent to Convert.ImplicitReferenceConversion
if (left.eclass == ExprClass.MethodGroup || right.eclass == ExprClass.MethodGroup)
return null;
type = TypeManager.bool_type;
GenericConstraints constraints;
bool lgen = TypeManager.IsGenericParameter (l);
if (TypeManager.IsEqual (l, r)) {
if (lgen) {
//
// Only allow to compare same reference type parameter
//
if (TypeManager.IsReferenceType (l)) {
left = new BoxedCast (left, TypeManager.object_type);
right = new BoxedCast (right, TypeManager.object_type);
return this;
}
return null;
}
if (l == InternalType.AnonymousMethod)
return null;
if (TypeManager.IsValueType (l))
return null;
return this;
}
bool rgen = TypeManager.IsGenericParameter (r);
//
// a, Both operands are reference-type values or the value null
// b, One operand is a value of type T where T is a type-parameter and
// the other operand is the value null. Furthermore T does not have the
// value type constrain
//
if (left is NullLiteral || right is NullLiteral) {
if (lgen) {
constraints = TypeManager.GetTypeParameterConstraints (l);
if (constraints != null && constraints.HasValueTypeConstraint)
return null;
left = new BoxedCast (left, TypeManager.object_type);
return this;
}
if (rgen) {
constraints = TypeManager.GetTypeParameterConstraints (r);
if (constraints != null && constraints.HasValueTypeConstraint)
return null;
right = new BoxedCast (right, TypeManager.object_type);
return this;
}
}
//
// An interface is converted to the object before the
// standard conversion is applied. It's not clear from the
// standard but it looks like it works like that.
//
if (lgen) {
if (!TypeManager.IsReferenceType (l))
return null;
l = TypeManager.object_type;
left = new BoxedCast (left, l);
} else if (l.IsInterface) {
l = TypeManager.object_type;
} else if (TypeManager.IsStruct (l)) {
return null;
}
if (rgen) {
if (!TypeManager.IsReferenceType (r))
return null;
r = TypeManager.object_type;
right = new BoxedCast (right, r);
} else if (r.IsInterface) {
r = TypeManager.object_type;
} else if (TypeManager.IsStruct (r)) {
return null;
}
const string ref_comparison = "Possible unintended reference comparison. " +
"Consider casting the {0} side of the expression to `string' to compare the values";
//
// A standard implicit conversion exists from the type of either
// operand to the type of the other operand
//
if (Convert.ImplicitReferenceConversionExists (left, r)) {
if (l == TypeManager.string_type)
ec.Report.Warning (253, 2, loc, ref_comparison, "right");
return this;
}
if (Convert.ImplicitReferenceConversionExists (right, l)) {
if (r == TypeManager.string_type)
ec.Report.Warning (252, 2, loc, ref_comparison, "left");
return this;
}
return null;
}
Expression ResolveGenericParameter (ResolveContext ec, Type d, Type t)
{
GenericConstraints constraints = TypeManager.GetTypeParameterConstraints (t);
if (constraints != null) {
if (constraints.IsReferenceType && TypeManager.IsStruct (d))
return CreateConstantResult (ec, false);
}
if (TypeManager.IsGenericParameter (expr.Type)) {
if (constraints != null && constraints.IsValueType && expr.Type == t)
return CreateConstantResult (ec, true);
expr = new BoxedCast (expr, d);
}
return this;
}
public override Expression DoResolve (ResolveContext ec)
{
// Because expr is modified
if (eclass != ExprClass.Invalid)
return this;
if (resolved_type == null) {
resolved_type = base.DoResolve (ec);
if (resolved_type == null)
return null;
}
type = probe_type_expr.Type;
eclass = ExprClass.Value;
Type etype = expr.Type;
if (!TypeManager.IsReferenceType (type) && !TypeManager.IsNullableType (type)) {
if (TypeManager.IsGenericParameter (type)) {
ec.Report.Error (413, loc,
"The `as' operator cannot be used with a non-reference type parameter `{0}'. Consider adding `class' or a reference type constraint",
probe_type_expr.GetSignatureForError ());
} else {
ec.Report.Error (77, loc,
"The `as' operator cannot be used with a non-nullable value type `{0}'",
TypeManager.CSharpName (type));
}
return null;
}
if (expr.IsNull && TypeManager.IsNullableType (type)) {
return Nullable.LiftedNull.CreateFromExpression (ec, this);
}
Expression e = Convert.ImplicitConversion (ec, expr, type, loc);
if (e != null){
expr = e;
do_isinst = false;
return this;
}
if (Convert.ExplicitReferenceConversionExists (etype, type)){
if (TypeManager.IsGenericParameter (etype))
expr = new BoxedCast (expr, etype);
do_isinst = true;
return this;
}
if (TypeManager.ContainsGenericParameters (etype) ||
TypeManager.ContainsGenericParameters (type)) {
expr = new BoxedCast (expr, etype);
do_isinst = true;
return this;
}
ec.Report.Error (39, loc, "Cannot convert type `{0}' to `{1}' via a built-in conversion",
TypeManager.CSharpName (etype), TypeManager.CSharpName (type));
return null;
}
Expression ResolveGenericParameter (Type d, Type t)
{
#if GMCS_SOURCE
GenericConstraints constraints = TypeManager.GetTypeParameterConstraints (t);
if (constraints != null) {
if (constraints.IsReferenceType && d.IsValueType)
return CreateConstantResult (false);
if (constraints.IsValueType && !d.IsValueType)
return CreateConstantResult (TypeManager.IsEqual (d, t));
}
if (!TypeManager.IsReferenceType (expr.Type))
expr = new BoxedCast (expr, d);
return this;
#else
return null;
#endif
}