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)
{
// UNDONE: This is a premature realization of the nullable conversion as
// UNDONE: a constructor. Rather than flagging this, can we simply emit it
// UNDONE: as a cast node and have the operator rewrite pass turn it into
// UNDONE: a constructor call?
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().nubLiftKind = NullableCallLiftKind.NullableConversionConstructor;
}
if (exprUDC != null)
{
exprUDC.UserDefinedCall = exprTmp;
exprUDC.setType((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);
EXPRMEMGRP 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.nubLiftKind = NullableCallLiftKind.NullableConversion;
exprDst.pConversions = exprDst.castOfNonLiftedResultToLiftedType;
exprDest = exprDst;
}
return(true);
}