Variadic Example

variadics.go

package main

import (
	"context"
	"errors"
	"fmt"
)

type (
	Service struct {
		logger interface{}
		db     interface{}
	}
	ServiceOption func(*Service) error
)

func WithLogger(logger interface{}) ServiceOption {
	return func(s *Service) error {
		if logger == nil {
			return errors.New("invalid logger")
		}

		s.logger = logger
	}
}

func NewService(options ...ServiceOption) (*Service, error) {
	s := &Service{
		db:     nil,
		logger: nil,
	}

	for _, opt := range options {
		if err := opt(s); err != nil {
			return nil, err
		}
	}

	return s, nil
}

type writeArgs struct {
	file   io.File
	logger interface{}
	db     interface{}
}

type Option func(args *writeArgs) error

func WithLogger(logger interface{}) Option {
	return func(args *writeArgs) error {
		if logger == nil {
			return errors.New("invalid logger")
		}

		args.logger = logger
	}
}

func (s *Service) Write(ctx context.Context, file io.File, options ...Option) error {
	args := &writeArgs{
		logger: s.logger,
		db:     s.db,
		file:   file,
	}

	for _, option := range options {
		if err := option(args); err != nil {
			return fmt.Errorf("failed to overwrite write arguments: %w", err)
		}
	}

	// do things with args

	return nil
}