NuGet.InstallWalker.OnAfterPackageWalk C# (CSharp) Method

        protected override void OnAfterPackageWalk(IPackage package)
        {
            if (!Repository.Exists(package))
            {
                // Don't add the package for installation if it already exists in the repository
                _operations.AddOperation(new PackageOperation(package, PackageAction.Install));
            }
            else
            {
                // If we already added an entry for removing this package then remove it 
                // (it's equivalent for doing +P since we're removing a -P from the list)
                _operations.RemoveOperation(package, PackageAction.Uninstall);
            }
        }