Use IDictionary instead of IReadOnlyDictionary before .NET 4.5

runtime/CSharp/Antlr4.Runtime/Dfa/AbstractEdgeMap`1.cs

@@ -103,7 +103,11 @@ namespace Antlr4.Runtime.Dfa
             get;
         }
 
+#if NET_4_5
         public abstract IReadOnlyDictionary<int, T> ToMap();
+#else
+        public abstract IDictionary<int, T> ToMap();
+#endif
 
         public virtual IEnumerator<KeyValuePair<int, T>> GetEnumerator()
         {

runtime/CSharp/Antlr4.Runtime/Dfa/ArrayEdgeMap`1.cs

@@ -168,7 +168,11 @@ namespace Antlr4.Runtime.Dfa
             return this;
         }
 
+#if NET_4_5
         public override IReadOnlyDictionary<int, T> ToMap()
+#else
+        public override IDictionary<int, T> ToMap()
+#endif
         {
             if (IsEmpty)
             {
@@ -183,7 +187,11 @@ namespace Antlr4.Runtime.Dfa
                 }
                 result[i + minIndex] = arrayData[i];
             }
+#if NET_4_5
             return new ReadOnlyDictionary<int, T>(result);
+#else
+            return result;
+#endif
         }
     }
 }

runtime/CSharp/Antlr4.Runtime/Dfa/DFAState.cs

@@ -221,7 +221,11 @@ namespace Antlr4.Runtime.Dfa
             }
         }
 
+#if NET_4_5
         public virtual IReadOnlyDictionary<int, DFAState> EdgeMap
+#else
+        public virtual IDictionary<int, DFAState> EdgeMap
+#endif
         {
             get
             {
@@ -265,7 +269,11 @@ namespace Antlr4.Runtime.Dfa
             }
         }
 
+#if NET_4_5
         public virtual IReadOnlyDictionary<int, DFAState> ContextEdgeMap
+#else
+        public virtual IDictionary<int, DFAState> ContextEdgeMap
+#endif
         {
             get
             {
@@ -273,7 +281,7 @@ namespace Antlr4.Runtime.Dfa
                 {
                     return Sharpen.Collections.EmptyMap<int, DFAState>();
                 }
-                IReadOnlyDictionary<int, DFAState> map = contextEdges.ToMap();
+                var map = contextEdges.ToMap();
                 if (map.ContainsKey(-1))
                 {
                     if (map.Count == 1)
@@ -285,7 +293,11 @@ namespace Antlr4.Runtime.Dfa
                         Dictionary<int, DFAState> result = map.ToDictionary(i => i.Key, i => i.Value);
                         result.Add(PredictionContext.EmptyFullStateKey, result[-1]);
                         result.Remove(-1);
+#if NET_4_5
                         map = new ReadOnlyDictionary<int, DFAState>(new SortedDictionary<int, DFAState>(result));
+#else
+                        map = new SortedDictionary<int, DFAState>(result);
+#endif
                     }
                 }
                 return map;

runtime/CSharp/Antlr4.Runtime/Dfa/IEdgeMap`1.cs

@@ -66,7 +66,12 @@ namespace Antlr4.Runtime.Dfa
         [return: NotNull]
         IEdgeMap<T> Clear();
 
+#if NET_4_5
         [return: NotNull]
         IReadOnlyDictionary<int, T> ToMap();
+#else
+        [return: NotNull]
+        IDictionary<int, T> ToMap();
+#endif
     }
 }

runtime/CSharp/Antlr4.Runtime/Dfa/SingletonEdgeMap`1.cs

@@ -149,7 +149,11 @@ namespace Antlr4.Runtime.Dfa
             return this;
         }
 
+#if NET_4_5
         public override IReadOnlyDictionary<int, T> ToMap()
+#else
+        public override IDictionary<int, T> ToMap()
+#endif
         {
             if (IsEmpty)
             {

runtime/CSharp/Antlr4.Runtime/Dfa/SparseEdgeMap`1.cs

@@ -201,7 +201,11 @@ namespace Antlr4.Runtime.Dfa
             return result;
         }
 
+#if NET_4_5
         public override IReadOnlyDictionary<int, T> ToMap()
+#else
+        public override IDictionary<int, T> ToMap()
+#endif
         {
             if (IsEmpty)
             {
@@ -212,7 +216,11 @@ namespace Antlr4.Runtime.Dfa
             {
                 result[keys[i]] = values[i];
             }
+#if NET_4_5
             return new ReadOnlyDictionary<int, T>(result);
+#else
+            return result;
+#endif
         }
     }
 }

runtime/CSharp/Antlr4.Runtime/Sharpen/Collections.cs

@@ -39,7 +39,11 @@ namespace Sharpen
             return EmptyListImpl<T>.Instance;
         }
 
+#if NET_4_5
         public static ReadOnlyDictionary<TKey, TValue> EmptyMap<TKey, TValue>()
+#else
+        public static IDictionary<TKey, TValue> EmptyMap<TKey, TValue>()
+#endif
         {
             return EmptyMapImpl<TKey, TValue>.Instance;
         }
@@ -49,9 +53,13 @@ namespace Sharpen
             return new ReadOnlyCollection<T>(new T[] { item });
         }
 
+#if NET_4_5
         public static ReadOnlyDictionary<TKey, TValue> SingletonMap<TKey, TValue>(TKey key, TValue value)
+#else
+        public static IDictionary<TKey, TValue> SingletonMap<TKey, TValue>(TKey key, TValue value)
+#endif
         {
-            return new ReadOnlyDictionary<TKey, TValue>(new Dictionary<TKey, TValue> { { key, value } });
+            return new Dictionary<TKey, TValue> { { key, value } };
         }
 
         private static class EmptyListImpl<T>
@@ -61,8 +69,18 @@ namespace Sharpen
 
         private static class EmptyMapImpl<TKey, TValue>
         {
+#if NET_4_5
             public static readonly ReadOnlyDictionary<TKey, TValue> Instance =
                 new ReadOnlyDictionary<TKey, TValue>(new Dictionary<TKey, TValue>());
+#else
+            public static IDictionary<TKey, TValue> Instance
+            {
+                get
+                {
+                    return new Dictionary<TKey, TValue>();
+                }
+            }
+#endif
         }
     }
 }