public static Expression ImplicitNullableConversion(ParseContext ec, Expression expr, Type targetType)
{
Type exprType = expr.Type;
//
// From null to any nullable type
//
if (exprType == TypeManager.CoreTypes.Null)
{
return(ec == null ? EmptyExpression.Null : LiftedNullExpression.Create(targetType, expr.Span));
}
// S -> T?
var elementType = targetType.GetGenericArguments()[0];
// S? -> T?
if (TypeManager.IsNullableType(exprType))
{
exprType = exprType.GetGenericArguments()[0];
}
//
// Predefined implicit identity or implicit numeric conversion
// has to exist between underlying type S and underlying type T
//
// Handles probing
if (ec == null)
{
if (exprType == elementType)
{
return(EmptyExpression.Null);
}
return(MakeImplicitNumericConversion(ec, null, exprType, elementType));
}
Expression unwrap;
if (exprType != expr.Type)
{
unwrap = Unwrap.Create(expr);
}
else
{
unwrap = expr;
}
Expression conv = exprType == elementType ? unwrap : MakeImplicitNumericConversion(ec, unwrap, exprType, elementType);
if (conv == null)
{
return(null);
}
if (exprType != expr.Type)
{
return(new LiftedExpression(conv, unwrap, targetType).Resolve(ec));
}
// Do constant optimization for S -> T?
if (unwrap is ConstantExpression)
{
conv = ((ConstantExpression)unwrap).ConvertImplicitly(elementType);
}
return(Wrap.Create(conv, targetType));
}