Use pattern matching in a few more places.

src/Compilers/CSharp/Portable/Compilation/SyntaxTreeSemanticModel.cs

@@ -507,7 +507,7 @@ private ConsList<TypeSymbol> GetBasesBeingResolved(TypeSyntax expression)
             for (; expression != null && expression.Parent != null; expression = expression.Parent as TypeSyntax)
             {
                 var parent = expression.Parent;
-                if (parent is BaseTypeSyntax && parent.Parent != null && parent.Parent.Kind() == SyntaxKind.BaseList && ((BaseTypeSyntax)parent).Type == expression)
+                if (parent is BaseTypeSyntax baseType && parent.Parent != null && parent.Parent.Kind() == SyntaxKind.BaseList && baseType.Type == expression)
                 {
                     // we have a winner
                     var decl = (BaseTypeDeclarationSyntax)parent.Parent.Parent;

src/Compilers/CSharp/Test/Symbol/Symbols/MockSymbolTests.cs

@@ -140,10 +140,10 @@ private void DumpSymbol(Symbol sym, StringBuilder builder, int level)
                 throw new InvalidOperationException("Unexpected symbol kind");
             }
 
-            if (sym is NamespaceOrTypeSymbol && ((NamespaceOrTypeSymbol)sym).GetMembers().Any())
+            if (sym is NamespaceOrTypeSymbol namespaceOrType && namespaceOrType.GetMembers().Any())
             {
                 builder.AppendLine(" { ");
-                var q = from c in ((NamespaceOrTypeSymbol)sym).GetMembers()
+                var q = from c in namespaceOrType.GetMembers()
                         orderby c.Name
                         select c;
 

src/ExpressionEvaluator/Core/Source/ExpressionCompiler/PDB/PdbHelpers.cs

@@ -194,7 +194,7 @@ public static ConstantValue GetSymConstantValue(ITypeSymbol type, object symValu
                     return ConstantValue.Create((double)symValue);
 
                 case SpecialType.System_String:
-                    if (symValue is int && (int)symValue == 0)
+                    if (symValue is int intVal1 && intVal1 == 0)
                     {
                         return ConstantValue.Null;
                     }
@@ -204,8 +204,7 @@ public static ConstantValue GetSymConstantValue(ITypeSymbol type, object symValu
                         return ConstantValue.Create(string.Empty);
                     }
 
-                    var str = symValue as string;
-                    if (str == null)
+                    if (!(symValue is string str))
                     {
                         return ConstantValue.Bad;
                     }
@@ -213,7 +212,7 @@ public static ConstantValue GetSymConstantValue(ITypeSymbol type, object symValu
                     return ConstantValue.Create(str);
 
                 case SpecialType.System_Object:
-                    if (symValue is int && (int)symValue == 0)
+                    if (symValue is int intVal2 && intVal2 == 0)
                     {
                         return ConstantValue.Null;
                     }
@@ -221,12 +220,12 @@ public static ConstantValue GetSymConstantValue(ITypeSymbol type, object symValu
                     return ConstantValue.Bad;
 
                 case SpecialType.System_Decimal:
-                    if (!(symValue is decimal))
+                    if (!(symValue is decimal decimalValue))
                     {
                         return ConstantValue.Bad;
                     }
 
-                    return ConstantValue.Create((decimal)symValue);
+                    return ConstantValue.Create(decimalValue);
 
                 case SpecialType.System_DateTime:
                     if (!(symValue is double))
@@ -239,7 +238,7 @@ public static ConstantValue GetSymConstantValue(ITypeSymbol type, object symValu
                 case SpecialType.None:
                     if (type.IsReferenceType)
                     {
-                        if (symValue is int && (int)symValue == 0)
+                        if (symValue is int intValue3 && intValue3 == 0)
                         {
                             return ConstantValue.Null;
                         }

src/Features/CSharp/Portable/Completion/CompletionProviders/ObjectInitializerCompletionProvider.cs

@@ -174,7 +174,7 @@ protected override HashSet<string> GetInitializedMembers(SyntaxTree tree, int po
 
         protected override bool IsInitializable(ISymbol member, INamedTypeSymbol containingType)
         {
-            if (member is IPropertySymbol && ((IPropertySymbol)member).Parameters.Any(p => !p.IsOptional))
+            if (member is IPropertySymbol property && property.Parameters.Any(p => !p.IsOptional))
             {
                 return false;
             }

src/VisualStudio/CSharp/Impl/LanguageService/CSharpHelpContextService.cs

@@ -163,7 +163,7 @@ private bool TryGetTextForSymbol(SyntaxToken token, SemanticModel semanticModel,
             }
 
             // Just use syntaxfacts for operators
-            if (symbol is IMethodSymbol && ((IMethodSymbol)symbol).MethodKind == MethodKind.BuiltinOperator)
+            if (symbol is IMethodSymbol method && method.MethodKind == MethodKind.BuiltinOperator)
             {
                 text = null;
                 return false;

src/Workspaces/Core/Portable/FindSymbols/FindReferences/Finders/AbstractReferenceFinder.cs

@@ -744,10 +744,10 @@ public override Task<ImmutableArray<Project>> DetermineProjectsToSearchAsync(ISy
             FindReferencesSearchOptions options, CancellationToken cancellationToken)
         {
             var symbol = symbolAndProjectId.Symbol;
-            if (symbol is TSymbol && CanFind((TSymbol)symbol))
+            if (symbol is TSymbol typedSymbol && CanFind(typedSymbol))
             {
                 return DetermineCascadedSymbolsAsync(
-                    symbolAndProjectId.WithSymbol((TSymbol)symbol),
+                    symbolAndProjectId.WithSymbol(typedSymbol),
                     solution, projects, options, cancellationToken);
             }
 

src/Workspaces/Core/Portable/FindSymbols/FindReferences/Finders/ParameterSymbolReferenceFinder.cs

@@ -211,7 +211,7 @@ private SyntaxNode GetContainer(SemanticModel semanticModel, SyntaxNode paramete
             {
                 var declaredSymbol = semanticModel.GetDeclaredSymbol(current);
 
-                if (declaredSymbol is IMethodSymbol && ((IMethodSymbol)declaredSymbol).MethodKind != MethodKind.AnonymousFunction)
+                if (declaredSymbol is IMethodSymbol method && method.MethodKind != MethodKind.AnonymousFunction)
                 {
                     return current;
                 }