private static bool IsVarianceUnsafe <T>(
TypeSymbol type,
bool requireOutputSafety,
bool requireInputSafety,
Symbol context,
LocationProvider <T> locationProvider,
T locationArg,
BindingDiagnosticBag diagnostics)
where T : Symbol
{
Debug.Assert(requireOutputSafety || requireInputSafety);
// A type T is "output-unsafe" ["input-unsafe"] if one of the following holds:
switch (type.Kind)
{
case SymbolKind.TypeParameter:
// 1) T is a contravariant [covariant] type parameter
TypeParameterSymbol typeParam = (TypeParameterSymbol)type;
if (requireInputSafety && requireOutputSafety && typeParam.Variance != VarianceKind.None)
{
// This sub-case isn't mentioned in the spec, because it's not required for
// the definition. It just allows us to give a better error message for
// type parameters that are both output-unsafe and input-unsafe.
diagnostics.AddVarianceError(typeParam, context, locationProvider, locationArg, MessageID.IDS_Invariantly);
return(true);
}
else if (requireOutputSafety && typeParam.Variance == VarianceKind.In)
{
// The is output-unsafe case (1) from the spec.
diagnostics.AddVarianceError(typeParam, context, locationProvider, locationArg, MessageID.IDS_Covariantly);
return(true);
}
else if (requireInputSafety && typeParam.Variance == VarianceKind.Out)
{
// The is input-unsafe case (1) from the spec.
diagnostics.AddVarianceError(typeParam, context, locationProvider, locationArg, MessageID.IDS_Contravariantly);
return(true);
}
else
{
return(false);
}
case SymbolKind.ArrayType:
// 2) T is an array type with an output-unsafe [input-unsafe] element type
return(IsVarianceUnsafe(((ArrayTypeSymbol)type).ElementType, requireOutputSafety, requireInputSafety, context, locationProvider, locationArg, diagnostics));
case SymbolKind.ErrorType:
case SymbolKind.NamedType:
var namedType = (NamedTypeSymbol)type;
// 3) (see IsVarianceUnsafe(NamedTypeSymbol))
return(IsVarianceUnsafe(namedType, requireOutputSafety, requireInputSafety, context, locationProvider, locationArg, diagnostics));
default:
return(false);
}
}