Why is "where T : class" required in this example?

Sample code :

using System.Collections.Generic;
using FileHelpers;

....
private void Save<T>(string destFilename,  IEnumerable<T> data) where T : class    
{
    var engine = new FileHelperEngine((typeof(T)));


    engine.HeaderText = engine.GetFileHeader(); 
    engine.WriteFile(destFilename, data); // XX
}

At line XX, the 2nd parameter to engine.WriteFile is expecting an IEnumerable<object>. This code works ok.

My question is, why is the "where T : class" constraint required on the method ? If I remove it, I get the compile time error :

Argument 2: cannot convert from
'System.Collections.Generic.IEnumerable<T>' to
'System.Collections.Generic.IEnumerable<object>'

I would have thought that everything was an "object", and so that the constraint was not necessary ?

Why is "where T : class" required in this example?

2 Answers