Abstractions first

SquidStd is built abstractions-first: code depends on contracts, and concrete backends are chosen at composition time. This is what makes a SquidStd application easy to test and easy to retarget.

Contract package plus provider packages

Each capability is a contract package paired with one or more provider packages. The contract package - *.Abstractions - defines the interfaces and DTOs. Provider packages implement them. Your application references the abstraction and depends on the provider only in the host project. See the architecture overview for how this shapes the package graph.

In-memory for tests, external for prod

Most capabilities ship an in-memory provider for tests and an external-backend provider for production:

• Messaging - in-memory, or SquidStd.Messaging.RabbitMq / SquidStd.Messaging.Sqs.
• Caching - in-memory, or SquidStd.Caching.Redis.
• Storage - file-backed, or SquidStd.Storage.S3 (S3 and MinIO).

Tests run fast and deterministically against the in-memory provider; production swaps in the external backend.

Swapping providers without touching call sites

Because call sites depend only on the contract, switching backends is a registration change in the host - container.AddInMemoryMessaging() versus container.AddRabbitMqMessaging(...) - with no edits to the code that publishes or consumes messages. See dependency injection for the registration pattern that makes the swap a one-line change.