C# declaration of generic type

Question

Is it possible to get the \"c# name\" of a type obtained with reflexion like:

System.Collections.Generic.List`1[[System.String, mscorlib, Version=4.0.0.0, Cultur         


        

Answer 1

You can examine the type to find out if it is nested or not and if it is generic constructed or a primitive type. In particular I've realized that nested generic types lists its generic arguments at the end of the type name string. That is mentioned in documentation Type.GetType Method (String).

I have partially solved the task and my solution passes the following tests.

        [TestMethod]
        public void Tests()
        {

            Assert.AreEqual("int",typeof(int).ToCSharpMethodReturnTypeName());
            Assert.AreEqual("int[]",typeof(int[]).ToCSharpMethodReturnTypeName());
            Assert.AreEqual("int?", typeof(int?).ToCSharpMethodReturnTypeName());

            Assert.AreEqual("UnitTypeFriendlyNamesExtensionsTest.Inner2>.SubInner,object>", typeof(Inner2>.SubInner,object>).ToCSharpMethodReturnTypeName());

            Assert.ThrowsException(()=> typeof(Inner2>.SubInner, object>).DeclaringType.ToCSharpMethodReturnTypeName());

            var t = typeof(TestGenericReturnType);
            var m = t.GetMethod("GetService");
            var tt = m.ReturnType;

            Assert.AreEqual("DateTime",tt.ToCSharpMethodReturnTypeName());

            Assert.AreEqual("IDictionary",typeof(IDictionary).ToCSharpMethodReturnTypeName());
            Assert.AreEqual("IList",typeof(IList).ToCSharpMethodReturnTypeName());
            Assert.AreEqual("UnitTypeFriendlyNamesExtensionsTest.Astruc?",typeof(Astruc?).ToCSharpMethodReturnTypeName());
            Assert.AreEqual("UnitTypeFriendlyNamesExtensionsTest.Inner", typeof(Inner).ToCSharpMethodReturnTypeName());
        }

The extensions class handles nested and generic constructed types as well as primitive types.

public static class TypeFriendlyNamesExtensions
{
    private static readonly Dictionary TypeToFriendlyName = new Dictionary
    {
        {typeof(string), "string"},
        {typeof(object), "object"},
        {typeof(bool), "bool"},
        {typeof(byte), "byte"},
        {typeof(char), "char"},
        {typeof(decimal), "decimal"},
        {typeof(double), "double"},
        {typeof(short), "short"},
        {typeof(int), "int"},
        {typeof(long), "long"},
        {typeof(sbyte), "sbyte"},
        {typeof(float), "float"},
        {typeof(ushort), "ushort"},
        {typeof(uint), "uint"},
        {typeof(ulong), "ulong"},
        {typeof(void), "void"}
    };

    public static string ToCSharpMethodReturnTypeName(this Type type)
    {
        var sb = new StringWriter();
        ToCSharpNameEntry2(sb, type);
        return sb.ToString();
    }

    private static void ToCSharpNameEntry2(TextWriter sb, Type type0)
    {
        var list = GetContainingTypeList(type0);
        var usedGenericArgumentCounter = 0;

        HandleNestedLevel(sb, list, 0, ref usedGenericArgumentCounter);
        foreach (var ix in Enumerable.Range(1, list.Count - 1))
        {
            sb.Write(".");
            HandleNestedLevel(sb, list, ix, ref usedGenericArgumentCounter);
        }
    }

    private static void HandleNestedLevel(TextWriter sb, IReadOnlyList list, int ix,
        ref int usedGenericArgumentCounter)
    {
        var type = list[ix];
        if (TypeToFriendlyName.TryGetValue(type, out string fname))
        {
            sb.Write(fname);
            return;
        }
        if (type.IsGenericParameter)
        {
            sb.Write(type.Name);
            return;
        }
        if (type.IsArray)
        {
            ToCSharpNameEntry2(sb, type.GetElementType());
            sb.Write("[]");
            return;
        }

        if (type.IsGenericType)
        {
            var innermostType = list[list.Count - 1];
            var args = list[list.Count - 1].GenericTypeArguments;
            if (!type.IsConstructedGenericType)
            {
                if (innermostType.IsConstructedGenericType)
                {
                    var sname = GetSname(type);
                    sb.Write(sname);
                    sb.Write("<");
                    ToCSharpNameEntry2(sb, args[usedGenericArgumentCounter++]);
                    var loopCounter = ((TypeInfo) type).GenericTypeParameters.Length;
                    while (0 < --loopCounter)
                    {
                        sb.Write(",");
                        ToCSharpNameEntry2(sb, args[usedGenericArgumentCounter++]);
                    }
                    sb.Write(">");
                    return;
                }
                throw new NotImplementedException();
            }
            if (typeof(Nullable<>) == type.GetGenericTypeDefinition())
            {
                ToCSharpNameEntry2(sb, args[0]);
                sb.Write("?");
                return;
            }
            var cname = GetSname(type);
            sb.Write(cname);
            sb.Write("<");
            ToCSharpNameEntry2(sb, args[usedGenericArgumentCounter++]);
            while (usedGenericArgumentCounter < args.Length)
            {
                sb.Write(",");
                ToCSharpNameEntry2(sb, args[usedGenericArgumentCounter++]);
            }
            sb.Write(">");
            return;
        }
        if (type.IsPointer)
        {
            ToCSharpNameEntry2(sb, type);
            sb.Write("*");
            return;
        }
        sb.Write(type.Name);
    }

    private static string GetSname(Type type)
    {
        var name = type.Name;
        return name.Substring(0, name.IndexOf('`'));
    }

    private static List GetContainingTypeList(Type type)
    {
        var list = new List {type};
        var t = type;
        while (t.IsNested)
        {
            t = t.DeclaringType;
            list.Insert(0, t);
        }
        return list;
    }

    private static void ToCSharpNameEntry(StringBuilder sb, Type type)
    {
        var genericTypeArguments = type.GenericTypeArguments;
        var usedGenericTypeCounter = 0;
        ToCSharpNameRecursive(sb, type, genericTypeArguments, ref usedGenericTypeCounter);
    }

    private static void ToCSharpNameRecursive(StringBuilder sb, Type type, IReadOnlyList genericTypeArguments,
        ref int genericTypesCounter)
    {
        if (TypeToFriendlyName.TryGetValue(type, out string res))
        {
            sb.Append(res);
            return;
        }

        HandleNonPriminiveTypes(sb, type, genericTypeArguments, ref genericTypesCounter);
    }

    private static void HandleNonPriminiveTypes(StringBuilder sb, Type type, IReadOnlyList typeGenericTypeArguments,
        ref int genericTypesCounter)
    {
        var list = new List();
        var t = type;
        list.Add(t);
        while (t.IsNested)
        {
            t = t.DeclaringType;
            list.Add(t);
        }
        list.Reverse();
        foreach (var type1 in list)
        {
            HandleNestedLevel(sb, type1, typeGenericTypeArguments, ref genericTypesCounter);
            sb.Append(".");
        }
        sb.Length -= 1;
    }

    private static void HandleNestedLevel(StringBuilder sb, Type type, IReadOnlyList typeGenericTypeArguments,
        ref int genericTypesCounter)
    {
        var name = type.Name;
        if (type.IsGenericType)
        {
            var info = type.GetTypeInfo();
            var def = info.GetGenericTypeDefinition();
            var psLength = info.IsConstructedGenericType
                ? info.GenericTypeArguments.Length
                : info.GenericTypeParameters.Length;
            if (typeof(Nullable<>) == def)
            {
                var type1 = typeGenericTypeArguments[genericTypesCounter++];
                ToCSharpNameEntry(sb, type1);
                sb.Append("?");
                return;
            }

            var n = name.Substring(0, name.IndexOf("`", StringComparison.InvariantCultureIgnoreCase));

            sb.Append(n);
            sb.Append("<");
            for (var i = 0; i < psLength; i++)
            {
                ToCSharpNameEntry(sb, typeGenericTypeArguments[genericTypesCounter++]);
                sb.Append(",");
            }
            sb.Length -= 1;
            sb.Append(">");
            return;
        }
        if (type.IsArray)
        {
            var type1 = type.GetElementType();
            ToCSharpNameEntry(sb, type1);
            sb.Append("[]");
            return;
        }
        sb.Append(name);
    }
}

I use the extension method while composing the source text to be compiled by Roslyn