Use Case Interactor

This module defines generalized contract of Use Case Interactor to enable The Clean Architecture in Go application.

Why?

Isolating transport layer from business logic reduces coupling and allows better control on both transport and business sides. For example the application needs to consume AMQP events and act on them, with isolated use case interactor it is easy to trigger same action with HTTP message (as a part of developer tools).

Use case interactors declare their ports and may serve as a source of information for documentation automation.

This abstraction is intended for use with automated transport layer, for example see REST.

Usage

Input/Output Definitions

// Configure use case interactor in application layer.
type myInput struct {
    Param1 int    `path:"param1" description:"Parameter in resource path." multipleOf:"2"`
    Param2 string `json:"param2" description:"Parameter in resource body."`
}

type myOutput struct {
    Value1 int    `json:"value1"`
    Value2 string `json:"value2"`
}

Classic API

u := usecase.NewIOI(new(myInput), new(myOutput), func(ctx context.Context, input, output interface{}) error {
    var (
        in  = input.(*myInput)
        out = output.(*myOutput)
    )

    if in.Param1%2 != 0 {
        return status.InvalidArgument
    }

    // Do something to set output based on input.
    out.Value1 = in.Param1 + in.Param1
    out.Value2 = in.Param2 + in.Param2

    return nil
})

Generic API with type parameters

With go1.18 and later (or gotip) you can use simplified generic API instead of classic API based on interface{}.

u := usecase.NewInteractor(func(ctx context.Context, input myInput, output *myOutput) error {
    if in.Param1%2 != 0 {
        return status.InvalidArgument
    }

    // Do something to set output based on input.
    out.Value1 = in.Param1 + in.Param1
    out.Value2 = in.Param2 + in.Param2

    return nil
})

Further Configuration And Usage

// Additional properties can be configured for purposes of automated documentation.
u.SetTitle("Doubler")
u.SetDescription("Doubler doubles parameter values.")
u.SetTags("transformation")
u.SetExpectedErrors(status.InvalidArgument)
u.SetIsDeprecated(true)

Then use configured use case interactor with transport/documentation/etc adapter.

For example with REST router:

// Add use case handler to router.
r.Method(http.MethodPost, "/double/{param1}", nethttp.NewHandler(u))