Merge "Document how properties work in defaults modules." am: 188236ff

type DefaultsModuleBase struct {

	DefaultableModuleBase

	defaultProperties []interface{}

}

// The common pattern for defaults modules is to register separate instances of

// the xxxProperties structs in the AddProperties calls, rather than reusing the

// ones inherited from Module.

//

// The effect is that e.g. myDefaultsModuleInstance.base().xxxProperties won't

// contain the values that have been set for the defaults module. Rather, to

// retrieve the values it is necessary to iterate over properties(). E.g. to get

// the commonProperties instance that have the real values:

//

//   d := myModule.(Defaults)

//   for _, props := range d.properties() {

//     if cp, ok := props.(*commonProperties); ok {

//       ... access property values in cp ...

//     }

//   }

//

// The rationale is that the properties on a defaults module apply to the

// defaultable modules using it, not to the defaults module itself. E.g. setting

// the "enabled" property false makes inheriting modules disabled by default,

// rather than disabling the defaults module itself.

type Defaults interface {

	Defaultable

	isDefaults() bool