with option

type Options struct {
    FieldA string
    FieldB string
    FieldC string
}
func defaultOptions() *Options {
    return &Options{}
}

type Option func(*Options)
func WithA(a string) Option {
    return func(o *Options) {
        o.FieldA = a
    }
}
func WithB(b string) Option {
    return func(o *Options) {
        o.FieldB = b
    }
}
func WithC(c string) Option {
    return func(o *Options) {
        o.FieldC = c
    }
}

package main
import "fmt"
func main() {
    doSomething()
    doSomething(WithA("this is the filed a"))
    doSomething(WithA("this is the filed a"), WithB("this is the filed b"))
    doSomething(WithA("this is the filed a"), WithB("this is the filed b"), WithC("this is the filed c"))
}
func doSomething(opts ...Option) {
    o := defaultOptions()
    for _, opt := range opts {
        opt(o)
    }
    fmt.Printf("%+v\n", o)
}

o