What's the meaning of "apostrophe + number" in the object type of properties with generics (eg. "Collection`1")?

Question

I have an object (MyObject) with a property (MyProperty). I want to get it's type name (i.e. String or MyClass etc.). I use:

PropertyInfo propInfo = typeof(MyObject).GetProperty("MyProperty");
Console.WriteLine(propInfo.PropertyType.Name);
Console.WriteLine(propInfo.PropertyType.FullName);

No problem with simple types, but when MyProperty is a generic type, I face problems on getting it's name (e.g. Collection<String>). It prints:

Collection`1

System.Collections.ObjectModel.Collection`1[[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]

What is that `1? And how can I obtain "Collection<String>"?

Collection`1 means a generic collection with 1 generic type parameter — Leom Burke, Jul 05 '11 at 14:27

score 11 · Accepted Answer · edited Mar 24 '21 at 12:04

The `1 means a generic type, with 1 generic parameter.

One way of getting the string is by using the System.CodeDom, as suggested by @LukeH:

using System;
using System.CodeDom;
using System.Collections.Generic;
using Microsoft.CSharp;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var p = new CSharpCodeProvider())
            {
                var r = new CodeTypeReference(typeof(Dictionary<string, int>));
                
                Console.WriteLine(p.GetTypeOutput(r));
            }
        }
    }
}

An alternative method is here. See below for @jaredpar's code:

public static string GetFriendlyTypeName(Type type) {
    if (type.IsGenericParameter)
    {
        return type.Name;
    }

    if (!type.IsGenericType)
    {
        return type.FullName;
    }

    var builder = new System.Text.StringBuilder();
    var name = type.Name;
    var index = name.IndexOf("`");
    builder.AppendFormat("{0}.{1}", type.Namespace, name.Substring(0, index));
    builder.Append('<');
    var first = true;
    foreach (var arg in type.GetGenericArguments())
    {
        if (!first)
        {
            builder.Append(',');
        }
        builder.Append(GetFriendlyTypeName(arg));
        first = false;
    }
    builder.Append('>');
    return builder.ToString();
}

You might want to handle Nullables, and you might want to add a space after the comma. — SLaks, Jul 05 '11 at 14:37
If you copy the complete source, you might want to credit JaredPar with more than just a link to the question... — Heinzi, Jul 05 '11 at 14:37

score 8 · Answer 2 · answered Jul 05 '11 at 14:26

8

This is a CLR internal typename.

The number is the number of generic type parameters, since types can be overloaded.
(Func`1 and Func`2 are different types)

There is no built-in way to get a C#-style typename, since the CLR has nothing to do with C#.

answered Jul 05 '11 at 14:26

SLaks

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You can actually get at the C#-style name using CodeDom, but I probably wouldn't bother! Something like `using (var p = new CSharpCodeProvider()) { var r = new CodeTypeReference(propInfo.PropertyType); Console.WriteLine(p.GetTypeOutput(r)); }` – LukeH Jul 05 '11 at 14:40
@LukeH: Looking at the source, that only handles arrays, not generics. – SLaks Jul 05 '11 at 14:42
3

@LukeH, i think that comment should be an answer. – George Duckett Jul 05 '11 at 14:45

score 0 · Answer 3 · answered Jul 05 '11 at 14:32

0

SLaks already explained what `1 means.

About your second question: You can obtain the name of the generic type parameters by using Type.GetGenericArguments:

if (propInfo.PropertyType.IsGenericType) {
    Type[] typeArguments = propInfo.PropertyType.GetGenericArguments();
    // typeArguments now contains an array of types ({String} in your example).
}

answered Jul 05 '11 at 14:32

Heinzi

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He wants a string, not an array of type parameters. – SLaks Jul 05 '11 at 14:33
@SLaks: Good point. I'll leave that as an exercise to the reader. ;-) – Heinzi Jul 05 '11 at 14:34

What's the meaning of "apostrophe + number" in the object type of properties with generics (eg. "Collection`1")?

3 Answers3

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