英文:
Possible to add an append method to a slice
问题
我有以下类似的类型结构：
type Set []*Element
func (set *Set) AppendElements(elements []*Elements) {
// ?
}
显然，简单地将元素追加到切片中并不是很有用。然而，实际的函数会接收一些值，执行一些业务逻辑，然后追加元素。然而，我面临的困难是，在方法内部对切片进行修改并不会实际改变切片对外部调用者的值，因为append方法会分配一个新的切片，而这个新切片对调用者是不可见的。
有没有一种方法可以在方法中追加到切片中，或者应该将切片包装在结构体中或其他方式？
package main
import "fmt"
type Element int
type Set []*Element
func (ptr *Set) AppendElements(elements []*Element) {
set := *ptr
set = append(set, elements...)
}
func main() {
i := Element(1)
var set Set
set.AppendElements([]*Element{&i})
for _, el := range set {
fmt.Println(el)
}
}
更具体地说，上述代码什么都不会打印出来。
英文:
I have something like the following type structure below:
type Set []*Element
func (set *Set) AppendElements(elements []*Elements) {
// ?
}
Obviously simply appending elements to a slice is not very useful. However, the actual function takes some value, does some business logic, and then appends the elements. However, I am facing the difficulty that modifications to the slice inside of the method to not actually change the value of the slice to outside callers, because the append method allocates a new slice that is not seen by the callers.
Is there a way to append to the slice in a method or should the slice be wrapped in a struct or something else?
package main
import "fmt"
type Element int
type Set []*Element
func (ptr *Set) AppendElements(elements []*Element) {
set := *ptr
set = append(set, elements...)
}
func main() {
i := Element(1)
var set Set
set.AppendElements([]*Element{&i})
for _, el := range set {
fmt.Println(el)
}
}
More specifically, the above prints nothing.
答案1
得分: 10
你正在修改切片，但是你没有将其重新分配给指针。
func (ptr *Set) AppendElements(elements []*Element) {
set := *ptr
set = append(set, elements...)
*ptr = set
}
通常情况下，可以直接在append语句中取消引用指针：
func (set *Set) AppendElements(elements []*Element) {
*set = append(*set, elements...)
}
英文:
You're modifying the slice, but you never assign it back to the pointer.
func (ptr *Set) AppendElements(elements []*Element) {
set := *ptr
set = append(set, elements...)
*ptr = set
}
Usually though, one would dereference the pointer directly in the append statement:
func (set *Set) AppendElements(elements []*Element) {
*set = append(*set, elements...)
}
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