C#•16mo ago

✅ Return Proper Dictionary

At the moment my return value is null.

public class Data
{
}

public class MyData : Data
{
}

public interface IHelper
{
    public Dictionary<string, T> GetDictionary<T>();
}

public class MyClass : IHelper
{
    public Dictionary<string, MyData> myData = new Dictionary<string, MyData>();

    public Dictionary<string, Data> GetDictionary<Data>()
    {
        return myData as Dictionary<string, Data>;
    }
}

public class Data
{
}

public class MyData : Data
{
}

public interface IHelper
{
    public Dictionary<string, T> GetDictionary<T>();
}

public class MyClass : IHelper
{
    public Dictionary<string, MyData> myData = new Dictionary<string, MyData>();

    public Dictionary<string, Data> GetDictionary<Data>()
    {
        return myData as Dictionary<string, Data>;
    }
}

15 Replies

Moods•16mo ago

Uh That’s because myData can’t be converted to a Dictionary<string, Data>

r2d25551OP•16mo ago

How would I fix it? c++ we use templates. . . And I was trying similar here.

Thinker•16mo ago

variance issue You can't convert a Dictionary<string, MyData> to a Dictionary<string, Data> even if MyData inherits from Data If you were using an IReadOnlyDictionary<string, Data> instead it would work.

r2d25551OP•16mo ago

Oh.

Moods•16mo ago

Is that interface covariant? The more you know

r2d25551OP•16mo ago

Okay, thank you for letting me. My syntax is correct then?

Thinker•16mo ago

(I think so at least) syntax is all fine

MODiX•16mo ago

Thinker

REPL Result: Failure

record Data {} 
record MyData : Data {} 

IReadOnlyDictionary<string, Data> dict = new Dictionary<string, MyData>();

record Data {} 
record MyData : Data {} 

IReadOnlyDictionary<string, Data> dict = new Dictionary<string, MyData>();

Exception: CompilationErrorException

- Cannot implicitly convert type 'System.Collections.Generic.Dictionary<string, MyData>' to 'System.Collections.Generic.IReadOnlyDictionary<string, Data>'. An explicit conversion exists (are you missing a cast?)

- Cannot implicitly convert type 'System.Collections.Generic.Dictionary<string, MyData>' to 'System.Collections.Generic.IReadOnlyDictionary<string, Data>'. An explicit conversion exists (are you missing a cast?)

Compile: 533.352ms | Execution: 0.000ms | React with ❌ to remove this embed.

Thinker•16mo ago

well nevermind then I guess

Moods•16mo ago

Why isn’t it though

Moods•16mo ago

r2d25551OP•16mo ago

It does seem extremely limited.

Thinker•16mo ago

I mean, variance is variance :/ We fortunately don't have C++ templates 😄

r2d25551OP•16mo ago

c# is not my strong suit. C++ is a different matter and would quite simple. Thank you both. I will keep looking at it and for another alternative.

Accord•16mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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✅ Return Proper Dictionary