parsing map[string]CustomStruct

[jack-evans]

Is it possible to parse the above automatically or do I need to parse it as a map[string]interface{} and then cast the interface{} to the struct I want?

[alecthomas]

If CustomStruct implements TextUnmarshaler it should be possible, I think.

[jack-evans]

so I have:

type (
        myStruct struct {
                // some other fields
		ServicesConfiguration map[string]ServiceConfig `embed:"" prefix:"svcscfg-" envprefix:"SVCSCFG_" required:"true"`
	}

	ServiceConfig struct {
		DatabaseName string        `env:"DB_NAME" json:"databaseName"`
		CacheTTL     time.Duration `env:"CACHE_TTL" json:"cacheTtl"`
		UseCache     bool          `env:"USE_CACHE" json:"useCache"`
	}
)

func (s *ServiceConfig) UnmarshalText(text []byte) error {
	return json.Unmarshal(text, &s)
}

and I get:

panic: reflect: call of reflect.Value.NumField on map Value

goroutine 1 [running]:
reflect.flag.mustBe(...)
	/usr/local/go/src/reflect/value.go:223
reflect.Value.NumField({0x1ac0be0, 0x24daec8, 0x7dbf778})
	/usr/local/go/src/reflect/value.go:1723 +0x8d
github.com/alecthomas/kong.flattenedFields({0x1ac0be0, 0x24daec8, 0x0})
	/Users/*****/go/pkg/mod/github.com/alecthomas/[email protected]/build.go:54 +0xcc
github.com/alecthomas/kong.flattenedFields({0x1bbe060, 0x24dae60, 0x19cfbda})
	/Users/*****/go/pkg/mod/github.com/alecthomas/[email protected]/build.go:89 +0x60e
github.com/alecthomas/kong.flattenedFields({0x1b1b8c0, 0x24dae60, 0x0})
	/Users/*****/go/pkg/mod/github.com/alecthomas/[email protected]/build.go:89 +0x60e
github.com/alecthomas/kong.buildNode(0xc0002c90e0, {0x1b1b8c0, 0x24dae60, 0x4}, 0x0, 0xc0001f0410)
	/Users/*****/go/pkg/mod/github.com/alecthomas/[email protected]/build.go:118 +0x165
github.com/alecthomas/kong.build(0xc0002c90e0, {0x1aaf9c0, 0x24dae60})
	/Users/*****/go/pkg/mod/github.com/alecthomas/[email protected]/build.go:28 +0x2b3
github.com/alecthomas/kong.New({0x1aaf9c0, 0x24dae60}, {0xc000031f40, 0x1, 0x1})
	/Users/*****/go/pkg/mod/github.com/alecthomas/[email protected]/kong.go:104 +0x3fd
github.com/alecthomas/kong.Parse({0x1aaf9c0, 0x24dae60}, {0xc000031f40, 0xc0000001a0, 0x200000003})
	/Users/*****/go/pkg/mod/github.com/alecthomas/[email protected]/global.go:9 +0x2c
main.main()
	/Users/*****/go/src/*****/main.go:68 +0xb8

it happens whether I remove the json tag or not

[jack-evans]

I basically want an environment variable/command arg where I can pass something like:

{
  "myApiService": {
    "useCache": true,
    "databaseName": "foo",
    "cacheTtl": "60m"
  },
  "myOtherApiService": {
    "useCache": true,
    "databaseName": "bar",
    "cacheTtl": "20m"
  }
}

Any Ideas appreciated 🙂

[alecthomas]

Ah hmmm. Can you try implementing https://pkg.go.dev/github.com/alecthomas/kong#MapperValue instead?

I think TextUnmarshaler should work though. I'll take a look.

That's going to be pretty awkward to pass as a command-line value though I think?

[jack-evans]

yeah agreed, I am wondering if a config file that gets loaded on start would be better... rather than for a CLI its for a component that has multiple related API services exposed and trying to configure it in a way that doesn't mean you have hundreds of Environment variables and CLI args.