/// <summary>
/// Does an expression of type <paramref name="expressionType"/> "match" a pattern that looks for
/// type <paramref name="patternType"/>?
/// 'true' if the matched type catches all of them, 'false' if it catches none of them, and
/// 'null' if it might catch some of them. For this test we assume the expression's value
/// isn't null.
/// </summary>
protected bool?ExpressionOfTypeMatchesPatternType(
TypeSymbol expressionType,
TypeSymbol patternType,
ref HashSet <DiagnosticInfo> useSiteDiagnostics)
{
if (expressionType == patternType)
{
return(true);
}
var conversion = _conversions.ClassifyBuiltInConversion(expressionType, patternType, ref useSiteDiagnostics);
// This is for classification purposes only; we discard use-site diagnostics. Use-site diagnostics will
// be given if a conversion is actually used.
switch (conversion.Kind)
{
case ConversionKind.Boxing: // a value of type int matches a pattern of type object
case ConversionKind.Identity: // a value of a given type matches a pattern of that type
case ConversionKind.ImplicitReference: // a value of type string matches a pattern of type object
return(true);
case ConversionKind.ImplicitNullable: // a value of type int matches a pattern of type int?
case ConversionKind.ExplicitNullable: // a non-null value of type "int?" matches a pattern of type int
// but if the types differ (e.g. one of them is type byte and the other is type int?).. no match
return(ConversionsBase.HasIdentityConversion(expressionType.StrippedType().TupleUnderlyingTypeOrSelf(), patternType.StrippedType().TupleUnderlyingTypeOrSelf()));
case ConversionKind.ExplicitEnumeration: // a value of enum type does not match a pattern of integral type
case ConversionKind.ExplicitNumeric: // a value of type long does not match a pattern of type int
case ConversionKind.ImplicitNumeric: // a value of type short does not match a pattern of type int
case ConversionKind.ImplicitTuple: // distinct tuple types don't match
case ConversionKind.NoConversion:
return(false);
case ConversionKind.ExplicitDynamic: // a value of type dynamic might not match a pattern of type other than object
case ConversionKind.ExplicitReference: // a narrowing reference conversion might or might not succeed
case ConversionKind.Unboxing: // a value of type object might match a pattern of type int
return(null);
default:
// other conversions don't apply (e.g. conversions from expression, user-defined) and should not arise
throw ExceptionUtilities.UnexpectedValue(conversion.Kind);
}
}
