通过反射从其字符串创建任何类型实例

Question

Imagine the following scenario:

A user passes a string to the application, which represents a .NET-Type, eg string or System.IntPtr . Assuming, that the application in question has access to the assemblies, in which the given Types are defined, it can create an instance of the given type based on the string.

I have managed to create such an application; the problem is only, that I am not (yet) able to create "complex" or "nested" types, eg:

• Generics like System.Tuple<string, System.Action>
• Arrays of T like int[] , System.IntPtr[] , etc...
• Pointer of T like int* , char** , Namespace.MyStruct* , etc...
• Any (possible) combination of the cases above

My question is: How can I create such nested type instances, when only given the string representation of the type (and of course all required assemblies)?

Do the .NET BCL contain some sort of string --> Type -parser? Or do I have to use some form of recursive regex-parser and Activator.CreateInstance ?

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EDIT №1:
As this question seems to be too broad, I will try to clarify myself:

I am able to create type instances for 'simple' types - I am, however, struggling to create type instances of 'complex' types, eg:

Type t1 = typeof(string).Assembly.GetType("System.String");
Type t2 = typeof(string).Assembly.GetType("System.Tuple<System.String, System.Int32>");
object obj1 = Activator.CreateInstance(t1);
object obj2 = Activator.CreateInstance(t2);

obj1 is an instance of string , but obj2 will fail, as the variable t2 is null (Meaning, that the second line in the given code was unable to find the 'complex' type).

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EDIT №2:
The usage of Type::MakeGenericType(Type[]) is obviously helpful, but how would be the easiest/fastest(?) way to create an instance of a type like this:
IEnumerable<Tuple<int[,], char[][], Dictionary<string, Func<int, int*, byte>>>>
I would have to write some kind of regex-based parser, which iterates recursively over the different sections of the given string....

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EDIT №3:
I have discovered System::CodeDom::CodeTypeReference and I am currently searching for a method to get the type based on a given CodeTypeReference -instance (which can be created using the type's string representation).

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EDIT №4: (sorry for all the edits)
I think I found my solution in this SO post .

Answer 1

I might be missing something, but it looks like you're looking for Reflection . Specifically, the GetType method. The documentation states the following about this method:

Gets the Type with the specified name, performing a case-sensitive search.

Then you will want to look at Activator.CreateInstance :

Creates an instance of the specified type using that type's default constructor

Before you create the instance for generic types, though, you'll be wanting to look at `Type.MakeGenericType' :

Substitutes the elements of an array of types for the type parameters of the current generic type definition and returns a Type object representing the resulting constructed type.

You might find the answers to this other question useful too: How to use Activator to create an instance of a generic Type and casting it back to that type?

Answer 2

I solved it (temporarily) as follows:

1. Check if the given string contains < or >
2. If so, parse the string according to the function given below ( ParseGeneric ) and continue recursively using the parsed tokens
3. If not, check for any occurrence of array brackets ( [] , [][] , [,] etc.)
4. Parse the type accordingly using a recursive Array::CreateInstance(Type,int[])
5. Check for any occurrence of pointer 'stars' ( * ) and parse the type accordingly using Marshal::StructureToPtr

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My ParseGeneric -method:

 public static Type FetchGenericType(string typestring) { Match m; if ((m = Regex.Match(typestring, )).Success) { string cls = m.Groups["class"].ToString(); string par = m.Groups["params"].Success ? m.Groups["params"].ToString() : ""; List<string> paramtypes = new List<string>(); int s = 0, e = 0; for (int i = 0, c = 0, l = par.Length; i < l; i++) switch (par[i]) { case ',': if (c > 0) goto default; paramtypes.Add(par.Substring(s, e)); s = i + 1; e = 0; break; case '<': ++c; goto default; case '>': --c; goto default; default: ++e; break; } // I know, that this is bad as hell, but what should I do instead? paramtypes.Add(par.Substring(s, e)); IEnumerable<Type> @params = from type in paramtypes where !string.IsNullOrWhiteSpace(type) select FetchGenericType(type); string paramstring = string.Join(", ", from type in @params select "[" + type.FullName + ", " + type.Assembly.GetName().Name + "]"); string result = @params.Count() == 0 ? cls : string.Format("{0}`{1}[{2}]", cls, @paramsCount(), paramstr); // The string has now the format '...List`1[[System.String, mscorlib]]' // or: 'System.Tuple[[System.Int32, mscorlib], [System.Object, mscorlib]]' ... return FetchType(result); } else return FetchType(typestring); } 

The function FetchType does some basic array bracket parsing and then fetches the type based on the resulted string by looking through the given assemblies.