How to declare a default value for a struct with kelseyhightower/envconfig?

Question

At the beginning, everything is going well.

I have a configuration to read from drivers with the help of the package github.com/kelseyhightower/envconfig

type NXConfig struct {
    Enable bool `default:"true"`
    NxRate time.Duration `default:"300ms"`
    NxDisconnectingChance int `default:"8"`
    NxDisconnectionDuration time.Duration `default:"25s"`
}

var nxConfig NXConfig
envconfig.Process("NX", &nxConfig)

conf = &Config{
    NxConfig: &nxConfig,
}

in dev/test mode, the default valuations allow the struct members to be ready for testing with true, 300ms, 8, 25ms.

---

But it comes that my config relies now on a generated Item type too.
I cannot enter this type to put default values in front of its variable members, because it's a generated type: it is shared, and it would have no sense. But I need it, however, to be initialized with default values.

I've attempted first:

type NXConfig struct {
    Enable bool `default:"true"`
    Item nx.ActivationData {IpAddress: "127.0.0.1", PortNumber: 3000, ItemId: "99", ItemType: "990"}
    NxRate time.Duration `default:"300ms"`
    NxDisconnectingChance int `default:"8"`
    NxDisconnectionDuration time.Duration `default:"25s"`
}

but nx.ActivationData stays with it's members having nil or 0.

I've attempted second:

type NXConfig struct {
    Enable bool
    Item nx.ActivationData
    NxRate time.Duration
    NxDisconnectingChance int
    NxDisconnectionDuration time.Duration
}

removing the default values in the struct, and creating a constructor:

func NewNXConfig() *NXSimulatorConfig {
    return &NXConfig{   Enable: true,
        Item: nx.ActivationData {IpAddress: "127.0.0.1", PortNumber: 3000, ItemId: "99", ItemType: "990"},
        NxRate: time.Duration(time.Millisecond) * time.Duration(300),
        NxDisconnectingChance: 8,
        NxDisconnectionDuration:  time.Duration(time.Millisecond) * time.Duration(25)}
}

And I have changed the final lines with:

var nxConfig *NXConfig = NewNXConfig()
envconfig.Process("NX", nxConfig)

conf = &Config{
    NxConfig: nxConfig,
}

It worked. But it was a long path...

How to declare a default value for a struct child member, from with its outside, with default?

How should have I written the
Item nx.ActivationData {IpAddress: "127.0.0.1", PortNumber: 3000, ItemId: "99", ItemType: "990"}
declaration in my parent struct, to make it assign its members?

Answer 1

The simplest way to achieve your config is to add a struct for the config of the nx.ActivationItem and than build the nx.ActivationItem from said config. As a bonus your config is now also explicit in it's expected values, rather than embedding a generated struct.

type NXConfig struct {
    Enable                  bool `default:"true"`
    Item                    NXActivationData
    NxRate                  time.Duration `default:"300ms"`
    NxDisconnectingChance   int           `default:"8"`
    NxDisconnectionDuration time.Duration `default:"25s"`
}

type NXActivationData struct {
    IpAddress  string `default:"127.0.0.1"`
    PortNumber int    `default:"3000"`
    ItemId     string `default:"99"`
    ItemType   string `default:"990"`
}

func (cfg *NXActivationData) build() nx.ActivationData {
    return nx.ActivationData{
        IpAddress:  cfg.IpAddress,
        PortNumber: cfg.PortNumber,
        ItemId:     cfg.ItemId,
        ItemType:   cfg.ItemType,
    }
}