Make Dtos immutable

[IvanAntipov]

The Problem

Immutable objects are safe to use.

Example:

void Foo(Dto dto)
{
   var res1 = service1.Bar(dto);
   var res2 = service2.Bar(dto);
   ...
   Some logic with res1
   ...
   Some logic with res2
   ...
}

If dto is immutable, one can safely remove or change the call to service1 and be sure, that logic related to res2 is not affected. But if dto is muttable, we have to investigate all possible call chains on service1 in order to make the refactoring, because I don't know in advance how dto is mutated during the call to service1.

The good practice is not to mutate objects which are passed as arguments to public methods. This makes maintenance much easier.

Currently, Dtos (under src/Application) are not immutable because they contain public setters fields of mutable types like IList

I'd like

Let's replace set with init Dtos.
Let's replace IList with IReadOnlyCollection all Dtos.

Alternatives you've considered

No alternatives :)

We can use arguably IReadonlyList instead of IReadOnlyCollection, but I would prefer the former because it is more minimalistic.