How to run delegate based on dictionary (C#)

Question

I have Mock class with below:

private readonly List<SomeObject> m_objectsList = new List<SomeObject>();

public Task<IList<Auto>> Todo(SomeParams params)
{
 IEnumerable<Auto> matches = m_objectsList.Select(GetMyObject);
 return Task.FromResult<IList<Auto>>(matches.ToArray());
}

private Auto GetMyObject(SomeObject s)
{
 Auto newAuto = new Auto
 {
     Id = s.Id,
     Name = s.Name,
 };    
 return newAuto;
}

This is working OK. Now I want to do like:

private readonly Dictionary<SomeObject, SomeParams> m_objectsList2 = 
                                                 new Dictionary<SomeObject, SomeParams>();

public Task<IList<Auto>> Todo2(SomeParams params)
{
 IEnumerable<Auto> matches = m_objectsList2.Select(GetMyObject2);
 return Task.FromResult<IList<Auto>>(matches.ToArray());
}

private Auto GetMyObject2(SomeObject s, SomeParams p)
 {
  Auto newAuto = new Auto();
     ....//some code
     return newAuto;
 }

but getting Compiler Error CS0411.

I don't see how your code can work. You have too many type errors. Why is the name `m_objectsList2` when it is `Dictionary<>`? Why do you think `GetMyObject2` matches the signature of the `Func<>` required as a paramter for `Select`? What are the types you haven't defined? — NetMage, Mar 01 '23 at 18:45

Guru Stron · Accepted Answer · 2023-03-01T15:11:44.703

1

Dictionary<TKey, TValue> implements IEnumerable<KeyValuePair<TKey, TValue>>, and compiler can't perform method group conversion to delegate due to type mismatch. Either switch from using method group to lambda:

IEnumerable<Auto> matches = m_objectsList2.Select(kvp => GetMyObject2(kvp.Key, kvp.Value));

Or change signature of the method (or add an overload):

private Auto GetMyObject2(KeyValuePair<SomeObject, SomeParams> kvp)
{
     var (s, p) = kvp; // use deconstruction
     // or for older compilers/framework versions
     // var s = kvp.Key;
     // var p = kvp.Value;
     Auto newAuto = new Auto();
     ....//some code
     return newAuto;
}

edited Mar 01 '23 at 15:11

answered Mar 01 '23 at 14:07

Guru Stron

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1

What delegate type do you expect the method group `GetMyObject2` to convert to here? – Jon Skeet Mar 01 '23 at 14:09
@JonSkeet missed that another method was used, thank you. Fixed. – Guru Stron Mar 01 '23 at 14:12
how to to deconstruction of var(s, p) = kvp? – 4est Mar 01 '23 at 14:37
@4est added code (commented out) for older compilers/.NET versions. – Guru Stron Mar 01 '23 at 15:12

score 0 · Answer 2 · answered Mar 01 '23 at 14:41

Can try modifying your Todo2

public Task<IList<Auto>> Todo2()
{
   // Removed params parameter as I don't see the usage. Please add back if you need it
    return Task.FromResult<IList<Auto>>(m_objectsList2.Select(p => GetMyObject2(p.Key, p.Value)).ToArray());
}

How to run delegate based on dictionary (C#)

2 Answers2