Golang Field.InitElem方法代碼示例

// processField gets leading name for the env variable and combines the current
// field's name and generates environemnt variable names recursively
func (e *EnvironmentLoader) processField(prefix string, field *structs.Field) error {
	fieldName := e.generateFieldName(prefix, field)

	switch {
	case field.Kind() == reflect.Struct && !implementsTextUnmarshaler(field):
		for _, f := range field.Fields() {
			if err := e.processField(fieldName, f); err != nil {
				return err
			}
		}
	case field.Kind() == reflect.Ptr:
		field.InitElem()
		return e.processField(prefix, field)
	default:
		v := os.Getenv(fieldName)
		if v == "" {
			return nil
		}

		if err := fieldSet(field, v); err != nil {
			return err
		}
	}

	return nil
}

// processField gets tagName and the field, recursively checks if the field has the given
// tag, if yes, sets it otherwise ignores
func (t *TagLoader) processField(tagName string, field *structs.Field) error {
	switch {
	case field.Kind() == reflect.Struct && !implementsTextUnmarshaler(field):
		for _, f := range field.Fields() {
			if err := t.processField(tagName, f); err != nil {
				return err
			}
		}
	case field.Kind() == reflect.Ptr:
		field.InitElem()
		return t.processField(tagName, field)
	default:
		defaultVal := field.Tag(t.DefaultTagName)
		if defaultVal == "" {
			return nil
		}

		err := fieldSet(field, defaultVal)
		if err != nil {
			return err
		}
	}

	return nil
}

// processField generates a flag based on the given field and fieldName. If a
// nested struct is detected, a flag for each field of that nested struct is
// generated too.
func (f *FlagLoader) processField(flagSet *flag.FlagSet, fieldName string, field *structs.Field) error {
	if !field.IsExported() {
		return nil
	}

	if f.CamelCase {
		fieldName = strings.Join(camelcase.Split(fieldName), "-")
	}

	switch {
	case field.Kind() == reflect.Struct && !implementsTextUnmarshaler(field):
		for _, ff := range field.Fields() {
			flagName := fieldName + "-" + ff.Name()

			if f.Flatten {
				// first check if it's set or not, because if we have duplicate
				// we don't want to break the flag. Panic by giving a readable
				// output
				flagSet.VisitAll(func(fl *flag.Flag) {
					if strings.ToLower(ff.Name()) == fl.Name {
						// already defined
						panic(fmt.Sprintf("flag '%s' is already defined in outer struct", fl.Name))
					}
				})

				flagName = ff.Name()
			}

			if err := f.processField(flagSet, flagName, ff); err != nil {
				return err
			}
		}
	case field.Kind() == reflect.Ptr:
		field.InitElem()
		return f.processField(flagSet, fieldName, field)
	default:
		// Add custom prefix to the flag if it's set
		if f.Prefix != "" {
			fieldName = f.Prefix + "-" + fieldName
		}

		flagSet.Var(newFieldValue(field), flagName(fieldName), flagUsage(fieldName))
	}

	return nil
}