C#•12mo ago•

5 replies

Inheritance or composition

This is going to be a long one, totally get it if nobody makes it to the end

I'm writing an open-source library for writing durable workflows, similar in principle to Azure Durable Functions, where you can write persistent workflows using async/await. However, unlike Durable Functions, my library introduces a dedicated awaitable type called

DTask

DTask

.
Because

DTask

DTask

requires infrastructural support, you can't just await one inside a regular async method. To run them, providers must implement its infrastructure components (for storage access, serialization, etc.). One of these components is called

DAsyncHost

DAsyncHost

and, as of today, is an abstract class: it exposes and implements some methods to interact with these durable tasks (

StartAsync

StartAsync

ResumeAsync

ResumeAsync

), but also defines several abstract callbacks that implementations must override. For example,

OnDelayAsync

OnDelayAsync

determines how to handle

DTask.Delay

DTask.Delay

OnSucceedAsync

OnSucceedAsync

defines what to do when a durable task completes. Link to the class: https://github.com/gianvitodifilippo/DTasks/blob/main/src/DTasks/Infrastructure/DAsyncHost.cs
I went with an abstract class so I could provide virtual methods with default implementations and add new features in the future without breaking existing implementations (thanks to virtuals). However, I'm not a big fan of abstract classes and I usually prefer composition over inheritance, and I’m starting to wonder if

DAsyncHost

DAsyncHost

should have been a concrete class that could instead be injected into those classes that today are its child classes. I'm struggling now even more because I want to add a new overload of the

StartAsync

StartAsync

method that allows callers to pass a context object that the host can access during the whole execution. To do so, I thought of adding a type parameter to the type (

DAsyncHost<TContext>

DAsyncHost<TContext>

) and a new

StartAsync(TContext context, ...)

StartAsync(TContext context, ...)

method, but this started to feel like a smell to me.

What are your thoughts? Have you had some experience with similar designs?

C#•12mo ago•

5 replies

giadif

Inheritance or composition

This is going to be a long one, totally get it if nobody makes it to the end

DTask

DTask

.
Because

DTask

DTask

DAsyncHost

DAsyncHost

and, as of today, is an abstract class: it exposes and implements some methods to interact with these durable tasks (

StartAsync

StartAsync

ResumeAsync

ResumeAsync

), but also defines several abstract callbacks that implementations must override. For example,

OnDelayAsync

OnDelayAsync

determines how to handle

DTask.Delay

DTask.Delay

OnSucceedAsync

OnSucceedAsync

DAsyncHost

DAsyncHost

should have been a concrete class that could instead be injected into those classes that today are its child classes. I'm struggling now even more because I want to add a new overload of the

StartAsync

StartAsync

method that allows callers to pass a context object that the host can access during the whole execution. To do so, I thought of adding a type parameter to the type (

DAsyncHost<TContext>

DAsyncHost<TContext>

) and a new

StartAsync(TContext context, ...)

StartAsync(TContext context, ...)

method, but this started to feel like a smell to me.

What are your thoughts? Have you had some experience with similar designs?

Inheritance or composition

Inheritance or composition

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