函数选项模式 

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package main

// CustomStruct your defined struct
type CustomStruct struct {
	a string
	b string
}

// func function type
type OptionFunc func(*CustomStruct)

// edit the value of a
func InsertA(a string) OptionFunc {
	return func(o *CustomStruct) {
		o.a = a
	}
}

// edit the value of b
func InsertB(b string) OptionFunc {
	if b == "" {
		b = "Default value B"
	}
	return func(o *CustomStruct) {
		o.b = b
	}
}

// return object
func NewObject(opts ...OptionFunc) *CustomStruct {
	o := &CustomStruct{}
	for _, opt := range opts {
		opt(o)
	}
	return o
}

func main() {
	myObject := NewObject(InsertA("Inserted value"), InsertB(""))
	println(myObject.b)
}