Universal way to generate some Go code from single description (like X-Macro in C).

_x-macro.go

// I was looking for some substitution for X-Macro C preprocessor trick (https://en.wikipedia.org/wiki/X_Macro).
// And this method copes with a problem in a lot more straightforward and powerful way.

// X-Macro version in C:
//
// #define SOME_STATES(_) \
//     _(SOME_STATE_NEW,         "NEW") \
//     _(SOME_STATE_IN_PROGRESS, "IN_PROGRESS") \
//     _(SOME_STATE_DONE,        "DONE")
//
// #define X(name, ...) name,
// enum {
//     SOME_STATES(X)
// };
// #undef X

data.yaml

some_states:
  - name: SomeStateNew
    val: SomeState = iota
    text: NEW
  - name: SomeStateInProgress
    text: IN_PROGRESS
  - name: SomeStateDone
    text: DONE

some_state.go

package somepkg

//go:generate sh -c "gotpl some_state.tpl -f data.yaml | gofmt >some_state.gen.go"

// for debug use: go:generate sh -c "gotpl some_state.tpl -f data.yaml | tee /dev/stderr | gofmt >some_state.gen.go"

some_state.tpl

package somepkg

import "errors"

const (
    {{- range .some_states}}
    {{.name}} {{.val}}
    {{- end}}
)

func (s SomeState) String() string {
    switch s {
    {{- range .some_states}}
    case {{.name}}:
        return "{{.text}}"
    {{- end}}
    }
    return "<unknown>"
}

func Parse(s string) (SomeState, error) {
    switch s {
    {{- range .some_states}}
    case "{{.text}}":
        return {{.name}}, nil
    {{- end}}
    }
    return SomeState(0), errors.New("unknown some state")
}