_,err   = config.Load(
    config.Defaults{Item: defaultCfg},                                   // use default values
    config.CfgFile{Path: "sampledata/example_test/example.config.json"}, // load config from file
    config.EnvVar{Prefix: "ENVPREFIX"},                                  // load a config value from an env
    config.Unmarshal{Item: &cfg},                                        // marshal result into cfg
)

Multiple config flags can be passed to the load function, and they will enable different features.

Struct annotations

Struct fields can be annotated to specify the field name in the configuration, e.g.

type customCfg struct {
	U string   `config:"user"`
	Pw string  `config:"password"`
}

Best practices

when mapping your configuration there are some consideration that will make your live easier:

Maps instead of slices

If you need a list of items it's recommended to use a map instead of a slice.

Explanation:

picture this scenario: you define a set of default values as a slice

val := []string{
    "a","b"
}

and now as an Env you want to add another one, you would need to both provide the original default + the new value

#!/bin/bash
export VAL="a,b,c"

now let's see the same scenario as a map

val := map[string]string{
    "a": "a",
    "b": "b",
}

the corresponding env var would be.

#!/bin/bash
export VAL_C="c"

this is specially important when you have a map of structs