Why isn't this code compiling?

Question

I'm writing a method to generate a DataTable taking as datasource a generic IEnumerable. I am trying to set a default value on the field if theres no value, with the code below:

private void createTable<T>(IEnumerable<T> MyCollection, DataTable tabela) 
        {
            Type tipo = typeof(T);

            foreach (var item in tipo.GetFields() )
            {
                tabela.Columns.Add(new DataColumn(item.Name, item.FieldType));
            }

            foreach (Pessoa recordOnEnumerable in ListaPessoa.listaPessoas)
            {
                DataRow linha = tabela.NewRow();

                foreach (FieldInfo itemField in tipo.GetFields())
                {
                    Type typeAux = itemField.GetType();

                    linha[itemField.Name] =
                        itemField.GetValue(recordOnEnumerable) ?? default(typeAux); 

                }
            }
        }

It's throwing this error:

The type or namespace name 'typeAux', could not be found (are you missing a using directive or an assembly reference?)

Why? Shouldn't the function "Default(Type)" return a default value for that type?

`default()` requires a named type, not a `Type` reference. For example, `default(int)`. — recursive, Aug 21 '13 at 00:30

score 1 · Accepted Answer · edited May 23 '17 at 11:44

1

How about returning null for reference types and Activator.CreateInstance for value types

public static object GetDefault(Type type)
{
   if(type.IsValueType)
   {
      return Activator.CreateInstance(type);
   }
   return null;
}

Reference: Programmatic equivalent of default(Type)

edited May 23 '17 at 11:44

Community

1
1

answered Aug 21 '13 at 05:28

Carbine

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score 0 · Answer 2 · answered Aug 21 '13 at 00:32

0

The default statement doesn't work with System.Type.

That being said, it seems more appropriate to leave that out, and use DBNull directly:

linha[itemField.Name] = itemField.GetValue(recordOnEnumerable) ?? DBNull.Value;

If the value is null, setting the result to null (which, in a DataRow, is DBNull.Value) seems appropriate.

answered Aug 21 '13 at 00:32

Reed Copsey

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but does that requirres that types like int, boolean etc be declared like Nullables?... – Marcel James Aug 21 '13 at 00:41
@WilnerAvila No - `itemField.GetValue` would only return null if the value was actually null. Could never happen with int, bool, etc – Reed Copsey Aug 21 '13 at 15:54

Why isn't this code compiling?

2 Answers2