Getting Started

Constago scans Go structs and generates type-safe names for their fields and tags. It can produce package constants, grouped accessor values, and methods that return metadata or the field’s runtime value.

Requirements

Constago v0.1.0 requires Go 1.23 or later.

Install the command

go install github.com/cohesivestack/constago@v0.1.0

Make sure the Go binary directory is on your PATH, then verify the command:

constago --help

You can also run a pinned version without installing it:

go run github.com/cohesivestack/constago@v0.1.0 --help

Create a struct

package model

type User struct {
  Name    string `json:"name" title:"Name"`
  Country string `json:"country" title:"Country"`
}

Configure Constago

Create constago.yaml in the directory where you will run the command:

input:
  dir: "."
  include:
    - "**/*.go"
  exclude:
    - "**/*_test.go"
    - "**/constago.gen.go"

output:
  file_name: "constago.gen.go"

elements:
  - name: "json"
    input:
      mode: "tag"
      tag_priority: ["json"]
    output:
      mode: "constant"
      format:
        prefix: "JSON"

  - name: "title"
    input:
      mode: "tag"
      tag_priority: ["title"]
    output:
      mode: "struct"
      format:
        prefix: "Title"

getters:
  - name: "metadata"
    returns: ["json", "title", ":value"]
    output:
      prefix: "Metadata"
      format: "pascal"

Keep the generated filename in input.exclude. Otherwise, a later run can scan the previous generated file because the default **/*.go include matches it.

Generate code

Run Constago from the directory containing the configuration file:

constago

The command discovers constago.yaml automatically. To use another path:

constago --config ./config/constago.yaml

For the User struct, the generated file contains:

const (
  JSONUserName    = "name"
  JSONUserCountry = "country"
)

var TitleUser = struct {
  Name    string
  Country string
}{
  Name:    "Name",
  Country: "Country",
}

func (_struct *User) MetadataName() (string, string, string) {
  return "name", "Name", _struct.Name
}

func (_struct *User) MetadataCountry() (string, string, string) {
  return "country", "Country", _struct.Country
}

Format the generated file and compile the package:

gofmt -w constago.gen.go
go test ./...

Choose what to generate next

Read Configuration for every key and default.
Use Select Files & Types to control scanning.
See Generate Elements for constants, grouped accessors, and transforms.
See Generate Getters for metadata and runtime-value methods.
Import Constago directly with the Library API.