https://blog.rafaelfernandez.dev/tags/hexagonal-architecture/ Recent content in Hexagonal-Architecture on Home Hugo -- gohugo.io en © 2026 Rafael Fernandez Wed, 01 Apr 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/criteria4s-4-your-domain-has-no-database/ Wed, 01 Apr 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/criteria4s-4-your-domain-has-no-database/ How to use T <: CriteriaTag as a hexagonal port so your domain layer never imports a dialect. The database becomes a deployment decision. https://blog.rafaelfernandez.dev/posts/criteria4s-4-your-domain-has-no-database/ Wed, 01 Apr 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/criteria4s-4-your-domain-has-no-database/ How to use T <: CriteriaTag as a hexagonal port so your domain layer never imports a dialect. The database becomes a deployment decision. https://blog.rafaelfernandez.dev/posts/tagless-final-is-denotational-semantics/ Tue, 03 Mar 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/tagless-final-is-denotational-semantics/ Every trait in your hexagonal architecture is a tagless-final algebra. Every impl is an interpreter. You have been writing denotational semantics without knowing it. We trace the connection from Kiselyov’s paper through Scala’s Cats-Effect to Rust’s port traits, and show why the pattern that academics call ‘finally tagless’ is the same pattern that practitioners call ‘dependency injection.’ https://blog.rafaelfernandez.dev/posts/todo-tui-rust-5-event-polling-edit-vertical-slice/ Sat, 28 Feb 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/todo-tui-rust-5-event-polling-edit-vertical-slice/ The rat serves the last course. We fix input lag with non-blocking event polling, add the edit feature as a full vertical slice from application layer to TUI, watch the state machine grow from 3 to 4 variants with compiler-guided safety, and close with the key takeaways from the entire migration. https://blog.rafaelfernandez.dev/posts/todo-tui-rust-3-events-terminal-safety-migration/ Sat, 21 Feb 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/todo-tui-rust-3-events-terminal-safety-migration/ The rat wires up the ears. We implement mode-specific event handlers with crossterm, redesign the key mapping to use a toggle instead of separate keys, solve the terminal restore problem with a capture-cleanup-return pattern, and run cargo test to discover that zero lines changed outside the adapter. https://blog.rafaelfernandez.dev/posts/todo-tui-rust-1-scaffolding-tui-adapter-state-machine/ Sat, 14 Feb 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/todo-tui-rust-1-scaffolding-tui-adapter-state-machine/ We start a new series by migrating the CLI adapter to a ratatui TUI. We set up the new dependencies, design the module structure under adapters/tui/, model the interaction modes as an enum to make invalid states unrepresentable, and solve the ownership puzzle of cloning a repository in a persistent session. https://blog.rafaelfernandez.dev/posts/traits-are-grammars-too-from-contract-design-to-formal-syntax/ Wed, 28 Jan 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/traits-are-grammars-too-from-contract-design-to-formal-syntax/ While revisiting the TaskRepository trait from the Todo CLI series, I realized I was doing more than drawing an architectural boundary. I was also defining what could be said across that boundary, which is much closer to grammar than I first admitted. https://blog.rafaelfernandez.dev/posts/todo-cli-rust-5-cli-to-tui-with-ratatui/ Mon, 26 Jan 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/todo-cli-rust-5-cli-to-tui-with-ratatui/ We close the series by exploring what it means to migrate from CLI to TUI with ratatui: how the interaction model changes, what frictions Rust introduces with ownership and &mut in a persistent event loop, and why hexagonal architecture absorbs the change without surgery. https://blog.rafaelfernandez.dev/posts/todo-cli-rust-4-building-cli-with-clap/ Thu, 22 Jan 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/todo-cli-rust-4-building-cli-with-clap/ We design the CLI layer with clap derive, typed argument parsing with ValueEnum and FromStr for UUIDs, subcommands as enums, global –output flag for dual table/json output, and errors propagated through layers down to stderr. https://blog.rafaelfernandez.dev/posts/todo-cli-rust-3-1-testing-strategy-technical-debt/ Sun, 18 Jan 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/todo-cli-rust-3-1-testing-strategy-technical-debt/ We analyze the repository’s testing strategy: behavior-driven tests for each adapter, isolation with tempdir, why there are no shared tests, and the technical debt we decided to document instead of hide. https://blog.rafaelfernandez.dev/posts/todo-cli-rust-3-json-persistence-contract-vs-implementation/ Thu, 15 Jan 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/todo-cli-rust-3-json-persistence-contract-vs-implementation/ Third part of the series: we define the persistence contract with a generic trait, implement two adapters (in-memory and JSON to disk), and delve into the difference between interface and implementation as the axis of hexagonal architecture.