Delegate doesn't seem to register 'params'

Question

The params keyword of C# allows equivalence between Array and parameter-list, does it not?

Sadly, in my implementation, this isn't the case.

private Entities queryType(String entitiesType, params KeyValuePair<String, object>[] values)
{
    addStandardHeaders();
    String query = parsePredicate(values);
    Task<HttpResponseMessage> filterTask = client.GetAsync(client.BaseAddress + RESTapi.ALMentitiesQuery(domain, project, entitiesType, query));
    Task.WaitAny(filterTask);
    //Callback:
    HttpResponseMessage result = filterTask.Result;
    if (result.IsSuccessStatusCode)
    {
        updateCookies(client.BaseAddress+RESTapi.ALMentitiesQuery(domain, project, entitiesType, query));
        mainHeaders.Clear();
        Task<Stream> output = result.Content.ReadAsStreamAsync();
        Task.WaitAny(output);
        //Callback:
        return (Entities)fromJSON(output.Result, typeof(Entities)); 
    }
    else
    {
        util.Exception exception = getException(result);
        throw new HttpException(exception.Title);
    }
}

The delegate:

public delegate Entities SubTypeQuery(String subType, params KeyValuePair<String, object>[] values);

In application:

public List<Run> getRuns()
{
    List<Entity> selection = ((Entities)subTypeSelector.DynamicInvoke(
        ALMObject.Run.entitiesName(),
        (new KeyValuePair<String, object>("testcycle-id", id))
    )).entities.ToList<Entity>();

    List<Run> runSet = new List<Run>();
    foreach (Entity element in selection)
        runSet.Add(new Run(element, subTypeSelector));
    return runSet;
}

At run-time I get a Type-Exception: "Cannot convert KeyValuePair<String, object> to KeyValuePair<String, object>[]". This renders params completely useless. Suggestions?

Please reduce this to a [mcve]. Most of the code you've provided is irrelevant, and you have't told us where the problem is. Using `KeyValuePair` instead of a simpler type also makes this more complicated than it needs to be. (I'd also strongly recommend that you start following .NET naming conventions.) — Jon Skeet, Jul 11 '17 at 10:49

score 2 · Answer 1 · answered Jul 11 '17 at 10:51

2

The params keyword of C# allows equivalence between Array and parameter-list, does it not?

When the C# (or VB) compiler is involved, yes. Not when you're using reflection.

The problem is that you're invoking the delegate dynamically - with reflection, basically. Reflection code doesn't take any notice of params. You either need to invoke the delegate directly (without DynamicInvoke) or create the array explicitly.

answered Jul 11 '17 at 10:51

Jon Skeet

1,421,763
867
9,128
9,194

If the compiler says 'delegate doesn't exist in the current context' what should I do? – Olivier10178 Jul 11 '17 at 11:14
@Olivier10178: Without knowing what your code looks like, that doesn't really help. You might want to ask a new question with a [mcve]. – Jon Skeet Jul 11 '17 at 12:19

InBetween · Accepted Answer · 2017-07-11T11:10:04.493

2

Why are you dynamically invoking? You seem to know the types of all the arguments.

Whats wrong with simply calling the delegate?

List<Entity> selection = ((Entities)subTypeSelector(
    ALMObject.Run.entitiesName(),
    (new KeyValuePair<String, object>("testcycle-id", id))
)).entities.ToList<Entity>();

edited Jul 11 '17 at 11:10

answered Jul 11 '17 at 10:54

InBetween

32,319
3
50
90

My compiler angers me; it resolves that, and says 'subTypeSelector doesn't exist in this context'. Any other thoughts? @InBetween – Olivier10178 Jul 11 '17 at 11:10
1

@Olivier10178 That seems to be an unrelated issue to the question at hand and the code you've posted. Try to create a minimal repro and post a new question. – InBetween Jul 11 '17 at 11:14
@InBtetween no wait; it says now that it's an uninvocable member. – Olivier10178 Jul 11 '17 at 11:17
what type should I reference the delegate as if I want to apply it?? 'Delegate' doesn't seem to work. – Olivier10178 Jul 11 '17 at 11:19
@Olivier10178 The type of `subTypeSelector` should be `SubTypeQuery`. – InBetween Jul 11 '17 at 11:19
`My compiler angers me` - it is odd that when you provided the code to us originally it compiled fine, but now it complains about that line. Did you perhaps change any other parts of the code? – mjwills Jul 11 '17 at 11:32

mjwills · Answer 3 · 2017-07-11T11:35:25.227

0

I would suggest changing:

new KeyValuePair<String, object>("testcycle-id", id)

to:

new [] { new KeyValuePair<String, object>("testcycle-id", id) }

See also How do I pass an object array into a method as individual parameters? .

edited Jul 11 '17 at 11:35

answered Jul 11 '17 at 10:44

mjwills

23,389
6
40
63

And how does that leverage `params` which is what the OP is asking about? If you dynamically invoke you *loose* the flexibility `params` offers. The question here is why he's dynamically invoking instead of invoking directly. – InBetween Jul 11 '17 at 11:05
As per Jon Skeet's answer, the OP cannot make use of params in a reflection-based scenario. My answer is merely to show him / her an alternative that he / she might consider using. – mjwills Jul 11 '17 at 11:07

Delegate doesn't seem to register 'params'

3 Answers3