This repository is a companion to the Dependency Composition that discusses an alternative approach to building services using a somewhat unconventional combination of TDD, partial application, and functions as the primary compositional unit. The article is written using Typescript examples, but this is a port for Go, which means the pattern is necessarily a little bit different.
- Each component module defines a type with its own dependent functions.
- At the top level of the injection is done via the
injection.go - Rather than constructors for components, modules expose a factory function that takes dependencies and returns either a "configured" function or component.
Typescript's structure typing makes some things possible that are not in a language like Go. Go has structural typing but it's very different. Fulfilling an interface contract consists of implementing matching functions for a given type. Unfortunately, in order to implement an interface, you need an underlying struct and that struct cannot be anonymous, requiring a number of structs that have no purpose other to bind to functions. The result was a ton of template code. Instead, I used structs and assigned functions to them. This is closer to how the Typescript code was implemented. The downside is, however, that structs are nominally typed, meaning two types are considered different even if they are identical in composition. The means I have to use literally the same type and since Go doesn't provide any mechanism to prevent Nil-assigned fields, the type system won't help you if you forget to bind a function. The resulting composition is clear, but it's non-idiomatic and the type safety a bit weak.
In summary, I think the basic TDD and module injection approach works, but I'd try to achieve it in a somewhat different. Given that I don't work with Go very much, I will most likely leave that as an exercise to the reader.
make test
make run
You should then be able to access the service endpoint at http://localhost:8080/vancouverbc/restaurants/recommended