I am trying to use a single variable for either an Examine search :

var Query = (!string.IsNullOrEmpty(Request.QueryString["query"])?Request.QueryString["query"]:"");

var listItems = @CurrentPage
                .Search(Request.QueryString["query"]);

or (depending on the parameters) a node.Children - but concatenating several

var rootnodeIdsAR = rootnodeIds.Split(',');

    var listItems = getnodeList(rootnodeIdsAR[0]).ToList(); 


    for(var nl = 1; nl < rootnodeIdsAR.Length;nl++){
        var listItemstmp = getnodeList(rootnodeIdsAR[nl]);
        listItems = listItems.Concat(listItemstmp).ToList();
    }

functions{
    public Umbraco.Web.Models.DynamicPublishedContentList getnodeList(string parentnodeId){
        var parentNode = Umbraco.Content(parentnodeId);
        Umbraco.Web.Models.DynamicPublishedContentList nList;
        nList= parentNode.Children
            .Where("Visible");
        return nList;
    }
}

Each of the abover works in isolation (ie by letting var listItems handle the type casting) but if I try to get them to work in the same view

ie

if(Query!=""){
    listItems = @CurrentPage
                    .Search(Query);
}else{
        listItems = getnodeList(rootnodeIdsAR[0]).ToList(); 


        for(var nl = 1; nl < rootnodeIdsAR.Length;nl++){
            var listItemstmp = getnodeList(rootnodeIdsAR[nl]);
            listItems = listItems.Concat(listItemstmp).ToList();
        }

}

then I have a problem as I can't declare listItems twice.

I can't seem to be able to cast one as the other.

The reason for the use of a single variable is so I can use the listItems later in various parts of the code)

Not sure if this possible : maybe I'm trying to be too clever!