public void AddDependent(IPackage package, IPackage dependency)
{
HashSet<IPackage> values;
if (!_dependents.TryGetValue(dependency, out values))
{
values = new HashSet<IPackage>(PackageEqualityComparer.IdAndVersion);
_dependents.Add(dependency, values);
}
// Add the current package to the list of dependents
values.Add(package);
}