Options Pattern in Golang

What ..?

Option pattern very powerful in terms of modify the behaviour of the function without changing the code.
It is a function programming pattern that is used to provide optional arguments to a function.

example when user want to pass additional parameter to a function in SDK, then it modifies the behaviour accordingly.

suppose we have struct name called config which contains below configs

type Config struct{
        url     string
        port    string
        timeout time.Duration
    }

and now our factory methods something like this.

func NewConfig(url string,port string, timout time.Duration) *Config{
    return &Config{
        port:port,
        url:url,
        timeout:timeout,            
    }       
}

But i want port and timeout to be optional parameters. only url i want to make it mandatory

let's define new type called Option

type Option func(*Config)

Option is a function that takes Config . By using this option will modify the Config

func WithPort(port string) Option{
    return func(c *Config){
        c.port = port
    }
}

func WithTimeout(timeout time.Duration) Option{
    return func(c *Config){
        c.timeout = timeout
    }
}

Option is just a function it takes the pointer and return the updated config. now we have set the desired values to our config. Let's update the Factory method

func NewConfig(url string, opts ...Option) *Config{
    config := &Config{
        url:url
    }
    for _, opt := range opts{
        opt(config)
    }
    return config
}

Client creates basic Config

appConfig := NewConfig("http://api.google.com")

Client creates url with port

appConfig := NewConfig("http://api.google.com", WithPort("3000"))

appConfig := NewConfig("http://api.google.com", WithPort("3000"), WithTimeout(30*time.Second))

Blog

Options Pattern in Golang

Srinivas Kandukuri

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