英文:
Append to slice of interfaces
问题
我正在编写一个文档生成器。其中有一个DocumentItem接口，它是文档的一部分。
type DocumentItem interface {compose() string}
例如，一个文档由段落和表格组成。
type Paragraph struct {text string}type Table struct{}
Paragraph和Table类型对应于DocumentItem接口。
func (p *Paragraph) compose() string {return ""}func (t *Table) compose() string {return ""}
Document类型包含content []*DocumentItem字段。
type Document struct {content []*DocumentItem}
我正在寻找一种方法，使NewParagraph()和NewTable()函数能够创建所需的数据类型并将它们添加到content字段中。
func (d *Document) NewParagraph() *Paragraph {p := Paragraph{}d.content = append(d.content, &p)return &p}func (d *Document) NewTable() *Table {t := Table{}d.content = append(d.content, &t)return &t}
我使用接口指针的切片，以便能够在将它们包含在文档中后修改相应的变量数据。
func (p *Paragraph) SetText(text string) {p.text = text}func main() {d := Document{}p := d.NewParagraph()p.SetText("lalala")t := d.NewTable()// ...}
但是我得到了编译器错误：
cannot use &p (type *Paragraph) as type *DocumentItem in appendcannot use &t (type *Table) as type *DocumentItem in append
如果我将类型转换为DocumentItem接口，我将失去对特定函数的访问权限，而这些函数在某些类型的情况下可能与其他类型不同。例如，对于段落，可以添加文本，对于表格，可以添加一行单元格，然后对单元格添加文本。
这种情况是否可能？
英文:
I'm writing a document generator. There is a DocumentItem interface - this is part of the document.
type DocumentItem interface {compose() string}
For example, a document consists of paragraphs and tables.
type Paragraph struct {text string}type Table struct{}
The Paragraph and Table types correspond to the DocumentItem interface.
func (p *Paragraph) compose() string {return ""}func (t *Table) compose() string {return ""}
The Document type contains the content []*DocumentItem field.
type Document struct {content []*DocumentItem}
I'm looking for a way that would allow NewParagraph() and NewTable() functions to create the necessary data types and add them to the content field.
func (d *Document) NewParagraph() *Paragraph {p := Paragraph{}d.content = append(d.content, &p)return &p}func (d *Document) NewTable() *Table {t := Table{}d.content = append(d.content, &t)return &t}
I use an slice of interface pointers in order to be able to modify the data in the corresponding variables after they are included in the document.
func (p *Paragraph) SetText(text string) {p.text = text}func main() {d := Document{}p := d.NewParagraph()p.SetText("lalala")t := d.NewTable()// ...}
But I get compiler errors:
cannot use &p (type *Paragraph) as type *DocumentItem in appendcannot use &t (type *Table) as type *DocumentItem in append
If I cast the types to an DocumentItem interface, I will lose access to specific functions, which in the case of one type may differ from the other. For example, add text to a paragraph and add a row of cells and then add text to cell for the table.
Is it possible at all?
Full example at https://play.golang.org/p/uJfKs5tJ98
答案1
得分: 4
不要使用指向接口的指针，只使用接口的切片：
content []DocumentItem
如果接口值中包装的动态值是指针，你不会丢失任何东西，你可以修改指向的对象。
这是唯一需要更改的地方。为了验证，我在最后添加了打印输出：
fmt.Printf("%+v", p)
输出结果（在Go Playground上尝试）：
&{text:lalala}
英文:
Don't use pointer to interface, only a slice of interfaces:
content []DocumentItem
If the dynamic value wrapped in the interface value is a pointer, you lose nothing, you will be able to modify the pointed object.
This was the only thing that had to be changed. To verify, I added printing at the end:
fmt.Printf("%+v", p)
Output (try it on the Go Playground):
&{text:lalala}
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