// Model your application's configuration using a Go struct.
type cfg struct {
    Parameter string
}

// Two sources of configuration to merge.
base := strings.NewReader("module: {parameter: foo}")
override := strings.NewReader("module: {parameter: bar}")

// Merge the two sources into a Provider. Later sources are higher-priority.
// See the top-level package documentation for details on the merging logic.
provider, err := config.NewYAML(config.Source(base), config.Source(override))
if err != nil {
    panic(err) // handle error
}

var c cfg
if err := provider.Get("module").Populate(&c); err != nil {
  panic(err) // handle error
}

fmt.Printf("%+v\n", c)
// Output:
// {Parameter:bar}