private bool bindExplicitConversionToTypeVar()
{
// 13.2.3 Explicit reference conversions
//
// For a type-parameter T that is known to be a reference type (25.7), the following
// explicit reference conversions exist:
//
// * From the effective base class C of T to T and from any base class of C to T.
// * From any interface-type to T.
// * From a type-parameter U to T provided that T depends on U (25.7).
Debug.Assert(_typeSrc != null);
Debug.Assert(_typeDest != null);
// NOTE: for the flags, we have to use EXPRFLAG.EXF_FORCE_UNBOX (not EXPRFLAG.EXF_REFCHECK) even when
// we know that the type is a reference type. The verifier expects all code for
// type parameters to behave as if the type parameter is a value type.
// The jitter should be smart about it....
if (_typeSrc.isInterfaceType() || _binder.canConvert(_typeDest, _typeSrc, CONVERTTYPE.NOUDC))
{
if (!_needsExprDest)
{
return(true);
}
// There is an explicit, possibly unboxing, conversion from Object or any interface to
// a type variable. This will involve a type check and possibly an unbox.
// There is an explicit conversion from non-interface X to the type var iff there is an
// implicit conversion from the type var to X.
if (_typeSrc.IsTypeParameterType())
{
// Need to box first before unboxing.
EXPR exprT;
EXPRCLASS exprObj = GetExprFactory().MakeClass(_binder.GetReqPDT(PredefinedType.PT_OBJECT));
_binder.bindSimpleCast(_exprSrc, exprObj, out exprT, EXPRFLAG.EXF_FORCE_BOX);
_exprSrc = exprT;
}
if (_needsExprDest)
{
_binder.bindSimpleCast(_exprSrc, _exprTypeDest, out _exprDest, EXPRFLAG.EXF_FORCE_UNBOX);
}
return(true);
}
return(false);
}
private bool bindImplicitConversionFromTypeVar(TypeParameterType tyVarSrc)
{
// 13.1.4
//
// For a type-parameter T that is known to be a reference type (25.7), the following implicit
// reference conversions exist:
//
// * From T to its effective base class C, from T to any base class of C, and from T to any
// interface implemented by C.
// * From T to an interface-type I in T's effective interface set and from T to any base
// interface of I.
// * From T to a type parameter U provided that T depends on U (25.7). [Note: Since T is known
// to be a reference type, within the scope of T, the run-time type of U will always be a
// reference type, even if U is not known to be a reference type at compile-time.]
// * From the null type (11.2.7) to T.
//
// 13.1.5
//
// For a type-parameter T that is not known to be a reference type (25.7), the following conversions
// involving T are considered to be boxing conversions at compile-time. At run-time, if T is a value
// type, the conversion is executed as a boxing conversion. At run-time, if T is a reference type,
// the conversion is executed as an implicit reference conversion or identity conversion.
//
// * From T to its effective base class C, from T to any base class of C, and from T to any
// interface implemented by C. [Note: C will be one of the types System.Object, System.ValueType,
// or System.Enum (otherwise T would be known to be a reference type and 13.1.4 would apply
// instead of this clause).]
// * From T to an interface-type I in T's effective interface set and from T to any base
// interface of I.
//
// 13.1.6 Implicit type parameter conversions
//
// This clause details implicit conversions involving type parameters that are not classified as
// implicit reference conversions or implicit boxing conversions.
//
// For a type-parameter T that is not known to be a reference type, there is an implicit conversion
// from T to a type parameter U provided T depends on U. At run-time, if T is a value type and U is
// a reference type, the conversion is executed as a boxing conversion. At run-time, if both T and U
// are value types, then T and U are necessarily the same type and no conversion is performed. At
// run-time, if T is a reference type, then U is necessarily also a reference type and the conversion
// is executed as an implicit reference conversion or identity conversion (25.7).
CType typeTmp = tyVarSrc.GetEffectiveBaseClass();
TypeArray bnds = tyVarSrc.GetBounds();
int itype = -1;
for (; ;)
{
if (binder.canConvert(typeTmp, typeDest, flags | CONVERTTYPE.NOUDC))
{
if (!needsExprDest)
{
return(true);
}
if (typeDest.IsTypeParameterType())
{
// For a type var destination we need to cast to object then to the other type var.
EXPR exprT;
EXPRCLASS exprObj = GetExprFactory().MakeClass(binder.GetReqPDT(PredefinedType.PT_OBJECT));
binder.bindSimpleCast(exprSrc, exprObj, out exprT, EXPRFLAG.EXF_FORCE_BOX);
binder.bindSimpleCast(exprT, exprTypeDest, out exprDest, EXPRFLAG.EXF_FORCE_UNBOX);
}
else
{
binder.bindSimpleCast(exprSrc, exprTypeDest, out exprDest, EXPRFLAG.EXF_FORCE_BOX);
}
return(true);
}
do
{
if (++itype >= bnds.Size)
{
return(false);
}
typeTmp = bnds.Item(itype);
}while (!typeTmp.isInterfaceType() && !typeTmp.IsTypeParameterType());
}
}
