private bool bindExplicitConversionFromNub()
{
Debug.Assert(_typeSrc != null);
Debug.Assert(_typeDest != null);
// If S and T are value types and there is a builtin conversion from S => T then there is an
// explicit conversion from S? => T that throws on null.
if (_typeDest.IsValType() && _binder.BindExplicitConversion(null, _typeSrc.StripNubs(), _exprTypeDest, _pDestinationTypeForLambdaErrorReporting, _flags | CONVERTTYPE.NOUDC))
{
if (_needsExprDest)
{
Expr valueSrc = _exprSrc;
// This is a holdover from the days when you could have nullable of nullable.
// Can we remove this loop?
while (valueSrc.Type.IsNullableType())
{
valueSrc = _binder.BindNubValue(valueSrc);
}
Debug.Assert(valueSrc.Type == _typeSrc.StripNubs());
if (!_binder.BindExplicitConversion(valueSrc, valueSrc.Type, _exprTypeDest, _pDestinationTypeForLambdaErrorReporting, _needsExprDest, out _exprDest, _flags | CONVERTTYPE.NOUDC))
{
VSFAIL("BindExplicitConversion failed unexpectedly");
return(false);
}
if (_exprDest.Kind == ExpressionKind.EK_USERDEFINEDCONVERSION)
{
_exprDest.asUSERDEFINEDCONVERSION().Argument = _exprSrc;
}
}
return(true);
}
if ((_flags & CONVERTTYPE.NOUDC) == 0)
{
return(_binder.bindUserDefinedConversion(_exprSrc, _typeSrc, _typeDest, _needsExprDest, out _exprDest, false));
}
return(false);
}
/***************************************************************************************************
* Called by BindImplicitConversion when the destination type is Nullable<T>. The following
* conversions are handled by this method:
*
* For S in { object, ValueType, interfaces implemented by underlying type} there is an explicit
* unboxing conversion S => T?
* System.Enum => T? there is an unboxing conversion if T is an enum type
* null => T? implemented as default(T?)
*
* Implicit T?* => T?+ implemented by either wrapping or calling GetValueOrDefault the
* appropriate number of times.
* If imp/exp S => T then imp/exp S => T?+ implemented by converting to T then wrapping the
* appropriate number of times.
* If imp/exp S => T then imp/exp S?+ => T?+ implemented by calling GetValueOrDefault (m-1) times
* then calling HasValue, producing a null if it returns false, otherwise calling Value,
* converting to T then wrapping the appropriate number of times.
*
* The 3 rules above can be summarized with the following recursive rules:
*
* If imp/exp S => T? then imp/exp S? => T? implemented as
* qs.HasValue ? (T?)(qs.Value) : default(T?)
* If imp/exp S => T then imp/exp S => T? implemented as new T?((T)s)
*
* This method also handles calling bindUserDefinedConverion. This method does NOT handle
* the following conversions:
*
* Implicit boxing conversion from S? to { object, ValueType, Enum, ifaces implemented by S }. (Handled by BindImplicitConversion.)
* If imp/exp S => T then explicit S?+ => T implemented by calling Value the appropriate number
* of times. (Handled by BindExplicitConversion.)
*
* The recursive equivalent is:
*
* If imp/exp S => T and T is not nullable then explicit S? => T implemented as qs.Value
*
* Some nullable conversion are NOT standard conversions. In particular, if S => T is implicit
* then S? => T is not standard. Similarly if S => T is not implicit then S => T? is not standard.
***************************************************************************************************/
private bool BindNubConversion(NullableType nubDst)
{
// This code assumes that STANDARD and ISEXPLICIT are never both set.
// bindUserDefinedConversion should ensure this!
Debug.Assert(0 != (~_flags & (CONVERTTYPE.STANDARD | CONVERTTYPE.ISEXPLICIT)));
Debug.Assert(_exprSrc == null || _exprSrc.Type == _typeSrc);
Debug.Assert(!_needsExprDest || _exprSrc != null);
Debug.Assert(_typeSrc != nubDst); // BindImplicitConversion should have taken care of this already.
AggregateType atsDst = nubDst.GetAts(GetErrorContext());
if (atsDst == null)
{
return(false);
}
// Check for the unboxing conversion. This takes precedence over the wrapping conversions.
if (GetSymbolLoader().HasBaseConversion(nubDst.GetUnderlyingType(), _typeSrc) && !CConversions.FWrappingConv(_typeSrc, nubDst))
{
// These should be different! Fix the caller if typeSrc is an AggregateType of Nullable.
Debug.Assert(atsDst != _typeSrc);
// typeSrc is a base type of the destination nullable type so there is an explicit
// unboxing conversion.
if (0 == (_flags & CONVERTTYPE.ISEXPLICIT))
{
return(false);
}
if (_needsExprDest)
{
_binder.bindSimpleCast(_exprSrc, _exprTypeDest, out _exprDest, EXPRFLAG.EXF_UNBOX);
}
return(true);
}
int cnubDst;
int cnubSrc;
CType typeDstBase = nubDst.StripNubs(out cnubDst);
ExprClass exprTypeDstBase = GetExprFactory().MakeClass(typeDstBase);
CType typeSrcBase = _typeSrc.StripNubs(out cnubSrc);
ConversionFunc pfn = (_flags & CONVERTTYPE.ISEXPLICIT) != 0 ?
(ConversionFunc)_binder.BindExplicitConversion :
(ConversionFunc)_binder.BindImplicitConversion;
if (cnubSrc == 0)
{
Debug.Assert(_typeSrc == typeSrcBase);
// The null type can be implicitly converted to T? as the default value.
if (_typeSrc.IsNullType())
{
// If we have the constant null, generate it as a default value of T?. If we have
// some crazy expression which has been determined to be always null, like (null??null)
// keep it in its expression form and transform it in the nullable rewrite pass.
if (_needsExprDest)
{
if (_exprSrc.isCONSTANT_OK())
{
_exprDest = GetExprFactory().CreateZeroInit(nubDst);
}
else
{
_exprDest = GetExprFactory().CreateCast(0x00, _typeDest, _exprSrc);
}
}
return(true);
}
Expr exprTmp = _exprSrc;
// If there is an implicit/explicit S => T then there is an implicit/explicit S => T?
if (_typeSrc == typeDstBase || pfn(_exprSrc, _typeSrc, exprTypeDstBase, nubDst, _needsExprDest, out exprTmp, _flags | CONVERTTYPE.NOUDC))
{
if (_needsExprDest)
{
ExprUserDefinedConversion exprUDC = exprTmp.Kind == ExpressionKind.EK_USERDEFINEDCONVERSION ? exprTmp.asUSERDEFINEDCONVERSION() : null;
if (exprUDC != null)
{
exprTmp = exprUDC.UserDefinedCall;
}
// This logic is left over from the days when T?? was legal. However there are error/LAF cases that necessitates the loop.
// typeSrc is not nullable so just wrap the required number of times. For legal code (cnubDst <= 0).
for (int i = 0; i < cnubDst; i++)
{
exprTmp = _binder.BindNubNew(exprTmp);
exprTmp.asCALL().NullableCallLiftKind = NullableCallLiftKind.NullableConversionConstructor;
}
if (exprUDC != null)
{
exprUDC.UserDefinedCall = exprTmp;
exprUDC.Type = (CType)exprTmp.Type;
exprTmp = exprUDC;
}
Debug.Assert(exprTmp.Type == nubDst);
_exprDest = exprTmp;
}
return(true);
}
// No builtin conversion. Maybe there is a user defined conversion....
return(0 == (_flags & CONVERTTYPE.NOUDC) && _binder.bindUserDefinedConversion(_exprSrc, _typeSrc, nubDst, _needsExprDest, out _exprDest, 0 == (_flags & CONVERTTYPE.ISEXPLICIT)));
}
// Both are Nullable so there is only a conversion if there is a conversion between the base types.
// That is, if there is an implicit/explicit S => T then there is an implicit/explicit S?+ => T?+.
if (typeSrcBase != typeDstBase && !pfn(null, typeSrcBase, exprTypeDstBase, nubDst, false, out _exprDest, _flags | CONVERTTYPE.NOUDC))
{
// No builtin conversion. Maybe there is a user defined conversion....
return(0 == (_flags & CONVERTTYPE.NOUDC) && _binder.bindUserDefinedConversion(_exprSrc, _typeSrc, nubDst, _needsExprDest, out _exprDest, 0 == (_flags & CONVERTTYPE.ISEXPLICIT)));
}
if (_needsExprDest)
{
MethWithInst mwi = new MethWithInst(null, null);
ExprMemberGroup pMemGroup = GetExprFactory().CreateMemGroup(null, mwi);
ExprCall exprDst = GetExprFactory().CreateCall(0, nubDst, _exprSrc, pMemGroup, null);
// Here we want to first check whether or not the conversions work on the base types.
Expr arg1 = _binder.mustCast(_exprSrc, typeSrcBase);
ExprClass arg2 = GetExprFactory().MakeClass(typeDstBase);
bool convertible;
if (0 != (_flags & CONVERTTYPE.ISEXPLICIT))
{
convertible = _binder.BindExplicitConversion(arg1, arg1.Type, arg2, typeDstBase, out arg1, _flags | CONVERTTYPE.NOUDC);
}
else
{
convertible = _binder.BindImplicitConversion(arg1, arg1.Type, arg2, typeDstBase, out arg1, _flags | CONVERTTYPE.NOUDC);
}
if (!convertible)
{
VSFAIL("bind(Im|Ex)plicitConversion failed unexpectedly");
return(false);
}
exprDst.CastOfNonLiftedResultToLiftedType = _binder.mustCast(arg1, nubDst, 0);
exprDst.NullableCallLiftKind = NullableCallLiftKind.NullableConversion;
exprDst.PConversions = exprDst.CastOfNonLiftedResultToLiftedType;
_exprDest = exprDst;
}
return(true);
}