/// <summary>
/// Infer the result type of the switch expression by looking for a common type.
/// </summary>
private TypeSymbol InferResultType(ImmutableArray <BoundSwitchExpressionArm> switchCases, DiagnosticBag diagnostics)
{
var seenTypes = PooledHashSet <TypeSymbol> .GetInstance();
var typesInOrder = ArrayBuilder <TypeSymbol> .GetInstance();
foreach (var @case in switchCases)
{
var type = @case.Value.Type;
if (!(type is null) && seenTypes.Add(type))
{
typesInOrder.Add(type);
}
}
HashSet <DiagnosticInfo> useSiteDiagnostics = null;
var commonType = BestTypeInferrer.GetBestType(typesInOrder, Conversions, ref useSiteDiagnostics);
diagnostics.Add(SwitchExpressionSyntax, useSiteDiagnostics);
if (commonType is null)
{
diagnostics.Add(ErrorCode.ERR_SwitchExpressionNoBestType, SwitchExpressionSyntax.Location);
commonType = CreateErrorType();
}
seenTypes.Free();
return(commonType);
}
/// <summary>
/// Infer the result type of the switch expression by looking for a common type
/// to which every arm's expression can be converted.
/// </summary>
private TypeSymbol?InferResultType(
ImmutableArray <BoundSwitchExpressionArm> switchCases,
BindingDiagnosticBag diagnostics
)
{
var seenTypes =
Symbols.SpecializedSymbolCollections.GetPooledSymbolHashSetInstance <TypeSymbol>();
var typesInOrder = ArrayBuilder <TypeSymbol> .GetInstance();
foreach (var @case in switchCases)
{
var type = @case.Value.Type;
if (type is object && seenTypes.Add(type))
{
typesInOrder.Add(type);
}
}
seenTypes.Free();
CompoundUseSiteInfo <AssemblySymbol> useSiteInfo = GetNewCompoundUseSiteInfo(
diagnostics
);
var commonType = BestTypeInferrer.GetBestType(
typesInOrder,
Conversions,
ref useSiteInfo
);
typesInOrder.Free();
// We've found a candidate common type among those arms that have a type. Also check that every arm's
// expression (even those without a type) can be converted to that type.
if (commonType is object)
{
foreach (var @case in switchCases)
{
if (
!this.Conversions.ClassifyImplicitConversionFromExpression(
@case.Value,
commonType,
ref useSiteInfo
).Exists
)
{
commonType = null;
break;
}
}
}
diagnostics.Add(SwitchExpressionSyntax, useSiteInfo);
return(commonType);
}
private TypeSymbol InferReturnType(ref HashSet <DiagnosticInfo> useSiteDiagnostics, out bool inferredFromSingeType)
{
int numberOfDistinctReturns;
var resultTypes = BlockReturns.GetReturnTypes(this.Body, out numberOfDistinctReturns);
inferredFromSingeType = numberOfDistinctReturns < 2;
TypeSymbol bestResultType;
if (resultTypes.IsDefaultOrEmpty)
{
bestResultType = null;
}
else if (resultTypes.Length == 1)
{
bestResultType = resultTypes[0];
}
else
{
bestResultType = BestTypeInferrer.InferBestType(resultTypes, this.Binder.Conversions, ref useSiteDiagnostics);
}
if (!Symbol.IsAsync)
{
return(bestResultType);
}
// Async:
if (resultTypes.IsEmpty)
{
// No return statements have expressions; inferred type Task:
return(this.Binder.Compilation.GetWellKnownType(WellKnownType.System_Threading_Tasks_Task));
}
if ((object)bestResultType == null || bestResultType.SpecialType == SpecialType.System_Void)
{
// If the best type was 'void', ERR_CantReturnVoid is reported while binding the "return void"
// statement(s).
return(null);
}
// Some non-void best type T was found; infer type Task<T>:
return(this.Binder.Compilation.GetWellKnownType(WellKnownType.System_Threading_Tasks_Task_T).Construct(bestResultType));
}
/// <summary>
/// Infer the result type of the switch expression by looking for a common type.
/// </summary>
private TypeSymbol InferResultType(ImmutableArray <BoundSwitchExpressionArm> switchCases, DiagnosticBag diagnostics)
{
var seenTypes = SpecializedCollections.GetPooledSymbolHashSetInstance <TypeSymbol>();
var typesInOrder = ArrayBuilder <TypeSymbol> .GetInstance();
foreach (var @case in switchCases)
{
var type = @case.Value.Type;
if (!(type is null) && seenTypes.Add(type))
{
typesInOrder.Add(type);
}
}
HashSet <DiagnosticInfo> useSiteDiagnostics = null;
var commonType = BestTypeInferrer.GetBestType(typesInOrder, Conversions, ref useSiteDiagnostics);
diagnostics.Add(SwitchExpressionSyntax, useSiteDiagnostics);
seenTypes.Free();
return(commonType);
}
private static TypeSymbol InferReturnType(
BoundBlock block,
Binder binder,
TypeSymbol delegateType,
bool isAsync,
ref HashSet <DiagnosticInfo> useSiteDiagnostics,
out RefKind refKind,
out bool inferredFromSingleType)
{
int numberOfDistinctReturns;
var resultTypes = BlockReturns.GetReturnTypes(block, out refKind, out numberOfDistinctReturns);
inferredFromSingleType = numberOfDistinctReturns < 2;
TypeSymbol bestResultType;
if (resultTypes.IsDefaultOrEmpty)
{
bestResultType = null;
}
else if (resultTypes.Length == 1)
{
bestResultType = resultTypes[0];
}
else
{
bestResultType = BestTypeInferrer.InferBestType(resultTypes, binder.Conversions, ref useSiteDiagnostics);
}
if (!isAsync)
{
return(bestResultType);
}
// For async lambdas, the return type is the return type of the
// delegate Invoke method if Invoke has a Task-like return type.
// Otherwise the return type is Task or Task<T>.
NamedTypeSymbol taskType = null;
var delegateReturnType = delegateType?.GetDelegateType()?.DelegateInvokeMethod?.ReturnType as NamedTypeSymbol;
if ((object)delegateReturnType != null)
{
NamedTypeSymbol builderType;
MethodSymbol createBuilderMethod;
if (delegateReturnType.IsCustomTaskType(out builderType, out createBuilderMethod))
{
taskType = delegateReturnType;
}
}
if (resultTypes.IsEmpty)
{
// No return statements have expressions; use delegate InvokeMethod
// or infer type Task if delegate type not available.
return((object)taskType != null && taskType.Arity == 0 ?
taskType :
binder.Compilation.GetWellKnownType(WellKnownType.System_Threading_Tasks_Task));
}
if ((object)bestResultType == null || bestResultType.SpecialType == SpecialType.System_Void)
{
// If the best type was 'void', ERR_CantReturnVoid is reported while binding the "return void"
// statement(s).
return(null);
}
// Some non-void best type T was found; use delegate InvokeMethod
// or infer type Task<T> if delegate type not available.
var taskTypeT = (object)taskType != null && taskType.Arity == 1 ?
delegateReturnType.ConstructedFrom :
binder.Compilation.GetWellKnownType(WellKnownType.System_Threading_Tasks_Task_T);
return(taskTypeT.Construct(bestResultType));
}
public static TypeSymbol InferBestType(ImmutableArray<TypeSymbol> types, ConversionsBase conversions, ref HashSet<DiagnosticInfo> useSiteDiagnostics)
{
var inferrer = new BestTypeInferrer(conversions);
return inferrer.GetBestType(types, ref useSiteDiagnostics);
}
public static TypeSymbol InferBestType(ImmutableArray <TypeSymbol> types, Conversions conversions, ref HashSet <DiagnosticInfo> useSiteDiagnostics)
{
var inferrer = new BestTypeInferrer(conversions);
return(inferrer.GetBestType(types, ref useSiteDiagnostics));
}