new api (#2)

aconfig.go

@@ -23,6 +23,7 @@ const (
 // Loader of user configuration.
 type Loader struct {
 	config  LoaderConfig
+	src     interface{}
 	fields  []*fieldData
 	flagSet *flag.FlagSet
 }
@@ -54,6 +55,52 @@ func NewLoaderFor(cfg interface{}, config LoaderConfig) *Loader {
 	return l
 }
 
+// Loader creates a new Loader based on a config.
+// Zero-value config is acceptable.
+func LoaderFor(src interface{}) *Loader {
+	return &Loader{src: src}
+}
+
+func (l *Loader) SkipDefaults() *Loader {
+	l.config.SkipDefaults = true
+	return l
+}
+
+func (l *Loader) SkipFiles() *Loader {
+	l.config.SkipFile = true
+	return l
+}
+
+func (l *Loader) SkipEnvironment() *Loader {
+	l.config.SkipEnv = true
+	return l
+}
+
+func (l *Loader) SkipFlags() *Loader {
+	l.config.SkipFlag = true
+	return l
+}
+
+func (l *Loader) WithFiles(files []string) *Loader {
+	l.config.Files = files
+	return l
+}
+
+func (l *Loader) WithEnvPrefix(prefix string) *Loader {
+	l.config.EnvPrefix = prefix
+	return l
+}
+
+func (l *Loader) WithFlagPrefix(prefix string) *Loader {
+	l.config.FlagPrefix = prefix
+	return l
+}
+
+func (l *Loader) Build() *Loader {
+	l.preLoad(l.src)
+	return l
+}
+
 func (l *Loader) preLoad(cfg interface{}) {
 	fields := getFields(cfg)
 

example_test.go

@@ -16,6 +16,30 @@ type MyConfig struct {
 	}
 }
 
+func Example_NewApi() {
+	loader := aconfig.LoaderFor(&MyConfig{}).
+		SkipDefaults().SkipFiles().SkipEnvironment().SkipFlags().
+		WithFiles([]string{"/var/opt/myapp/config.json"}).
+		WithEnvPrefix("APP").
+		WithFlagPrefix("app").
+		Build()
+
+	var cfg MyConfig
+	if err := loader.Load(&cfg); err != nil {
+		log.Panic(err)
+	}
+
+	fmt.Printf("Port:      %v\n", cfg.Port)
+	fmt.Printf("Auth.User: %q\n", cfg.Auth.User)
+	fmt.Printf("Auth.Pass: %q\n", cfg.Auth.Pass)
+
+	// Output:
+	//
+	// Port:      0
+	// Auth.User: ""
+	// Auth.Pass: ""
+}
+
 // Just load defaults from struct defenition.
 //
 func Example_Defaults() {