C# class separation into a header and a .cs file

public interface IFoo
{
  int DoFoo();
}

pubic class Foo : IFoo
{
  public int DoFoo()
  {
    return 1;
  }
}

public sealed class Cache : IEnumerable
{
    // Fields
    private CacheInternal _cacheInternal;
    public static readonly DateTime NoAbsoluteExpiration;
    public static readonly TimeSpan NoSlidingExpiration;

    // Methods
    static Cache();
    [SecurityPermission(SecurityAction.Demand, Unrestricted=true)]
    public Cache();
    internal Cache(int dummy);
    public object Add(string key, object value, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback);
    public object Get(string key);
    internal object Get(string key, CacheGetOptions getOptions);
    public IDictionaryEnumerator GetEnumerator();
    public void Insert(string key, object value);
    public void Insert(string key, object value, CacheDependency dependencies);
    public void Insert(string key, object value, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration);
    public void Insert(string key, object value, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback);
    public object Remove(string key);
    internal void SetCacheInternal(CacheInternal cacheInternal);
    IEnumerator IEnumerable.GetEnumerator();

    // Properties
    public int Count { get; }
    public long EffectivePercentagePhysicalMemoryLimit { get; }
    public long EffectivePrivateBytesLimit { get; }
    public object this[string key] { get; set; }
}