Type.FullName returns null when …

returns null when the type is not generic type definition but contains generic paramters.

The rational behind this design is to ensure Type.FullName (if not null) can uniquely
identify a type in an assembly; or given the string returned by Type.FullName, href="http://msdn2.microsoft.com/en-us/library/system.type.gettype.aspx">Type.GetType(string
typeName) can return the original type back. It is hard to keep this invariant if

!type.IsGenericTypeDefinition && type.ContainsGenericParameters.

For instance, suppose we have an assembly compiled with the following C# code:

class G<T> {
    public void M<S>() { }


typeof(G<>).FullName is "G`1", and we can round trip this type from Type.GetType("G`1").
But we can build more complicated generic types, such as G<S> (type G<>
bound with the generic parameter from the method M<>); in order to identify
such type with a string, a lot of extra information is need.

Below are some examples where Type.FullName returns null.

class G<T> {
  public class C
{ }
  public void M(C
arg) { }
class G2<T> : class="cstype">G<T> { }

string s1 = typeof( class="cstype">G<>).GetGenericArguments()[0].FullName;

// T in G<T>: generic parameter

string s2 = typeof( class="cstype">G<>).GetMethod("M").GetParameters()[0].ParameterType.FullName;

// check out the IL, it is G`1/C<!T> (not generic type
// Related topic, see

string s3 = typeof( class="cstype">G2<>).BaseType.FullName;

// base type of G2<>, which is not generic type definition
// it equals to typeof(G<>).MakeGenericType(typeof(G2<>).GetGenericArguments()[0])

Comments (2)
  1. Wayne says:

    Yes, I discovered this the hard way, when some of my .NET 1.1 code broke when I tried to apply it to generics.  I’ve worked around it, and now it’s good to know why Microsoft did it this way.

  2. Kathy Kam says:

    Answer: It will assert.

    Why: &amp;nbsp;Well, first of all… there is one big reason why the assert would…

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