Question

For example:

DataTable table = new DataTable() 
{ 
  Columns = new DataColumnCollection(
     { 
         new DataColumn("col1"), 
         new DataColumn("col2")
     })
});

Answer 1

You are talking about the Collection Initialiser
feature added in C# 3. It is done like this:

DataTable table = new DataTable() 
{ 
    Columns = 
    { 
        new DataColumn("col1"), 
        new DataColumn("col2")
    }
};

This does not call a collection constructor, it uses the collection which already exists in the DataTable.

This is short-hand for Columns.Add(), so it doesn’t require Columns to have a setter.

You were so close with the code in your question!