Is there an easy way to cast between two List<T>?

Question

var candidates = (from l in db.GetLeads(lat, lon, role, radius + 10)
                  orderby l.Distance
                  select l);
        return (List<CandidateResult>)candidates;

Answer 1

If I understand your question correctly, you can use the Cast extension method, i.e.:

return candidates.Cast<CandidateResult>();

Answer 2

What about:

var candidates = (from l in db.GetLeads(lat, lon, role, radius + 10)
                  orderby l.Distance
                  select l).ToList();

Answer 3

Well, your "candidates" variable isn't a List<T> - it's an IEnumerable<T> for some T.

However, List<T> isn't variant in T even in C# 4 (as it's a class, and classes are invariant; and also because it uses T in both an input and an output position).

Your simplest solution is to get the right type of sequence to start with and then call ToList:

var candidates = (from l in db.GetLeads(lat, lon, role, radius + 10)
                  orderby l.Distance
                  select (CandidateResult) l);
return candidates.ToList();

You can call Cast instead if you want, as shown below but in this particular case I don't think it makes it any nicer.

var candidates = (from l in db.GetLeads(lat, lon, role, radius + 10)
                  orderby l.Distance
                  select l);
return candidates.Cast<CandidateResult>()
                 .ToList();

Note that when you're only really doing one thing (ordering in this case) it's often simpler not to use query expressions, e.g.

return db.GetLeads(lat, lon, role, radius + 10)
         .OrderBy(l => l.Distance)
         .Cast<CandidateResult>()
         .ToList();