Enable serialization IEnumerable<T> and IReadOnlyDictionary<T> descendants that have constructor with relevant collection

[Alezy80]

Is your feature request related to a problem? Please describe.

I have heavy usage of IReadOnlyCollection and IReadOnlyDictionary descendants in my code and confused, why I can serialize (IReadOnlyCollection<int>)myCollection, but can't serialize myCollection itself? And also I can't deserialize some collections, because they doesn't have ICollection<T> interface (which is overengineered).

Describe the solution you'd like.

I think, that collections that have constructor with parameter of IEnumerable<T> or its descendants must be serialized/deserialized from out the box. Also any IReadOnlyDictionary object having constructor with parameter of IDictionary/IReadOnlyDictionary must be supported.

Describe alternatives you've considered

I can write formatters for each collection, but that's has some issues:

1. I need to write some boilerplate code by hand, which is not fun.
2. It tends to reference MessagePack by DTO library. I don't want that.

[Alezy80]

Can anyone review this, or reject if the idea is weird?

[AArnott]

This looks good. I am a bit concerned because a class that happens to implement a collection interface may not be simply a collection, but it is in the last checks of the dynamic resolver, so risk of regression seems minimal.

[AArnott]

I think you have the IsAssignableFrom backwards. If the ctor allowed MyCustomDictionary, then IDictionary<K,V> may be assignable from it, but ultimately our Activator.CreateInstance call would fail because our Dictionary<K,V> object cannot be assigned to MyCustomDictionary

If you swap it to be:

if (parameters.Length == 1 && parameters[0].ParameterType.IsAssignableFrom(typeof(Dictionary<,>).MakeGenericType(keyType, valueType))

Then we know definitively that the ultimate invocation should succeed, and all the 3 types you were previously checking individually will all just work.

[AArnott]

Same here: it's backwards.

[AArnott]

Looks good. Although detecting IEnumerable<T> in an arbitrary object could lead to false matches, also matching on the constructor signature as you're doing seems like it will lead to a high match. And if it ever misses, the user can always specify the formatter to use.

[neuecc]

Thank you, I think it's good.