Use var except when casting

Author: GrahamTheCoder

CodeConverter/CSharp/MethodBodyExecutableStatementVisitor.cs

@@ -561,7 +561,9 @@ public override async Task<SyntaxList<StatementSyntax>> VisitForEachBlock(VBSynt
                 type = declaration.Type;
                 id = declaration.Variables.Single().Identifier;
             } else if (_semanticModel.GetSymbolInfo(stmt.ControlVariable).Symbol is ISymbol varSymbol) {
-                type = CommonConversions.GetTypeSyntax(varSymbol.GetSymbolType(), varSymbol.GetSymbolType()?.SpecialType == SpecialType.System_Object);
+                var variableType = varSymbol.GetSymbolType();
+                var useVar = variableType?.SpecialType == SpecialType.System_Object || _semanticModel.GetTypeInfo(stmt.Expression).ConvertedType.IsEnumerableOfExactType(variableType);
+                type = CommonConversions.GetTypeSyntax(varSymbol.GetSymbolType(), useVar);
                 var v = (IdentifierNameSyntax)await stmt.ControlVariable.AcceptAsync(_expressionVisitor);
                 if (_localsToInlineInLoop.Contains(varSymbol)) {
                     id = v.Identifier;

CodeConverter/Util/ITypeSymbolExtensions.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Linq;
+using ICSharpCode.CodeConverter.Util.FromRoslyn;
 using Microsoft.CodeAnalysis;
 
 namespace ICSharpCode.CodeConverter.Util
@@ -48,6 +49,20 @@ public static bool IsArrayOf(this ITypeSymbol t, SpecialType specialType)
         {
             return t is IArrayTypeSymbol ats && ats.ElementType.SpecialType == specialType;
         }
+
+        public static bool IsEnumerableOfExactType(this ITypeSymbol symbol, ITypeSymbol typeArg)
+        {
+            return SymbolEquivalenceComparer.Instance.Equals(GetEnumerableElementTypeOrDefault(symbol), typeArg);
+        }
+
+        private static ITypeSymbol GetEnumerableElementTypeOrDefault(ITypeSymbol symbol)
+        {
+            if (symbol is IArrayTypeSymbol ats) return ats.ElementType;
+            if (symbol is INamedTypeSymbol nt) return nt.Yield().Concat(nt.AllInterfaces).OfType<INamedTypeSymbol>()
+                .OnlyOrDefault(impl => impl.MetadataName == "IEnumerable`1")
+                ?.TypeArguments.OnlyOrDefault();
+            return null;
+        }
     }
 }
 

Tests/CSharp/StatementTests/LoopStatementTests.cs

@@ -174,7 +174,7 @@ internal partial class TestClass
 {
     private void TestMethod(int[] values)
     {
-        foreach (int v in values)
+        foreach (var v in values)
         {
             if (v == 2)
                 continue;
@@ -205,7 +205,7 @@ internal partial class TestClass
     private void TestMethod(int[] values)
     {
         var val = default(int);
-        foreach (int currentVal in values)
+        foreach (var currentVal in values)
         {
             val = currentVal;
             if (val == 2)
@@ -235,7 +235,7 @@ internal partial class TestClass
 {
     private void TestMethod(int[] values)
     {
-        foreach (int val in values)
+        foreach (var val in values)
         {
             if (val == 2)
                 continue;
@@ -269,12 +269,12 @@ internal partial class TestClass
     private void TestMethod(int[] values)
     {
         int keep1 = default, keep2;
-        foreach (int inline1 in values)
+        foreach (var inline1 in values)
         {
-            foreach (int currentKeep1 in values)
+            foreach (var currentKeep1 in values)
             {
                 keep1 = currentKeep1;
-                foreach (int inline2 in values)
+                foreach (var inline2 in values)
                 {
                     if (inline2 == 2)
                         continue;
@@ -397,7 +397,7 @@ internal partial class Program
     public static void Main(string[] args)
     {
         object zs = new[] { 1, 2, 3 };
-        foreach (object z in (IEnumerable)zs)
+        foreach (var z in (IEnumerable)zs)
             Console.WriteLine(z);
     }
 }");