Go struct构造函数中具有默认值的可选参数 [英] Optional parameters with defaults in Go struct constructors
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问题描述
我发现自己使用以下模式来获取Go struct构造函数中具有默认值的可选参数:
I've found myself using the following pattern as a way to get optional parameters with defaults in Go struct constructors:
package main
import (
"fmt"
)
type Object struct {
Type int
Name string
}
func NewObject(obj *Object) *Object {
if obj == nil {
obj = &Object{}
}
// Type has a default of 1
if obj.Type == 0 {
obj.Type = 1
}
return obj
}
func main() {
// create object with Name="foo" and Type=1
obj1 := NewObject(&Object{Name: "foo"})
fmt.Println(obj1)
// create object with Name="" and Type=1
obj2 := NewObject(nil)
fmt.Println(obj2)
// create object with Name="bar" and Type=2
obj3 := NewObject(&Object{Type: 2, Name: "foo"})
fmt.Println(obj3)
}
是是更好的方法来允许使用默认值的可选参数吗?
Is there a better way of allowing for optional parameters with defaults?
推荐答案
Dave Cheney为此提供了一个不错的解决方案覆盖默认值:
Dave Cheney offered a nice solution to this where you have functional options to overwrite defaults:
https://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis
因此您的代码将变为:
package main
import (
"fmt"
)
type Object struct {
Type int
Name string
}
func NewObject(options ...func(*Object)) *Object {
// Setup object with defaults
obj := &Object{Type: 1}
// Apply options if there are any
for _, option := range options {
option(obj)
}
return obj
}
func WithName(name string) func(*Object) {
return func(obj *Object) {
obj.Name = name
}
}
func WithType(newType int) func(*Object) {
return func(obj *Object) {
obj.Type = newType
}
}
func main() {
// create object with Name="foo" and Type=1
obj1 := NewObject(WithName("foo"))
fmt.Println(obj1)
// create object with Name="" and Type=1
obj2 := NewObject()
fmt.Println(obj2)
// create object with Name="bar" and Type=2
obj3 := NewObject(WithType(2), WithName("foo"))
fmt.Println(obj3)
}
https://play.golang.org/p/pGi90d1eI52
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