Why is the code's structure splitted into OrchardCore.XXXX and OrchardCore.XXXX.Abstractions

[HengzheLi]

I sow almost the orchardcore components whose code are splitted into two projects: OrchardCore.XXXX and OrchardCore.XXX.Abstractions.

Some components, like logging and localization, do have multiple impletementation. But a lot of components have only one impletementation for its Abstraction. This doubles the project count.

What is the concept behind this?

[hishamco]

The code is splitted into OrchardCore.XXXX.Abstractions and OrchardCore.XXXX is something align to ASP.NET Core APIs style

Some components, like logging and localization, do have multiple implementation. But a lot of components have only one implementation for its Abstraction. This doubles the project count.

For Module / Extension that may have multiple implementation, you will have at least one implementation out of the box, such as Localization, OrchardCore.Localization.Abstractions and OrchardCore.Localization.PortableObjects but you could have something like OrchardCore.Localization.Json .. etc. Please have a look to Microsoft.Extensions.XXX to see the style in more details

Sometimes you can find OrchardCore.XXXX.Core where this the core / default implementation like what we have in Email & Feed modules

[hishamco]

FYI this pattern will allow you to extend the framework and replace the default implementation to meet your requirements instead of merge the abstraction and implementation in one project