英文:
Duck typing in Go
问题
[]myint无法传递给Join，因为它不是fmt.Stringer类型，所以我必须写成：
parts := []fmt.Stringer{myint(1), myint(5), myint(6)}
但是如果我需要在另一个操作中使用parts，其中的值必须是整数，我应该将myint的切片转换为Stringer的切片吗？
英文:
I want to write a Join function that takes arbitrary objects with a String() method:
package mainimport ("fmt""strings")type myint intfunc (i myint) String() string {return fmt.Sprintf("%d", i)}func main() {parts := []myint{myint(1), myint(5), myint(6)}fmt.Println(Join(parts, ", "))}func Join(parts []fmt.Stringer, sep string) string {stringParts := make([]string, len(parts))for i, part := range(parts) {stringParts [i] = part.String()}return strings.Join(stringParts , sep)}
http://play.golang.org/p/EhkbyibzHw
[]myint cannot be passed to Join, because it is not of type fmt.Stringer, so I have to write:
parts := []fmt.Stringer{myint(1), myint(5), myint(6)}
But what if I need parts for another operation where the values have to be ints? Should I cast a slice of myint to a slice of Stringer then?
答案1
得分: 6
在Go语言中，没有强制类型转换，只有类型转换。但是，从具体的非接口类型的切片到接口类型的切片的转换是不可能的，除非在循环中显式地进行转换。原因是，例如在你的情况下，[]myint的底层数组与[]fmt.Stringer的内存布局不同。(相关FAQ)
另外，你不必写成：
parts := []myint{myint(1), myint(5), myint(6)}
以下写法也可以：
parts := []myint{1, 5, 6}
英文:
> Q: Should I cast a slice of myint to a slice of Stringer then?
There are no casts in Go - only conversions. But conversion from a slice of concrete, non interface type to a slice of interface type is not possible, except by doing it explicitly in a loop. The reason is that, as for example in your case, the []myint backing array has a different memory layout than []fmt.Stringer has. (Related FAQ)
On a side note, you don't have to write:
parts := []myint{myint(1), myint(5), myint(6)}
This should work identically:
parts := []myint{1, 5, 6}
答案2
得分: 1
将Join函数改为
func Join(sep string, parts ...fmt.Stringer) string {}
会使得代码更加简洁：
package mainimport ("fmt""strings")type myint intfunc (i myint) String() string {return fmt.Sprintf("%d", i)}type myfloat float32func (f myfloat) String() string {return fmt.Sprintf("%0.2f", f)}func main() {fmt.Println(Join(", ", myint(3), myfloat(3.5543)))}func Join(sep string, parts ...fmt.Stringer) string {stringParts := make([]string, len(parts))for i, part := range parts {stringParts[i] = part.String()}return strings.Join(stringParts, sep)}
英文:
Change the Join function to
func Join(sep string, parts ...fmt.Stringer) string {}
makes it a lot easier:
package mainimport ("fmt""strings")type myint intfunc (i myint) String() string {return fmt.Sprintf("%d", i)}type myfloat float32func (f myfloat) String() string {return fmt.Sprintf("%0.2f", f)}func main() {fmt.Println(Join(", ", myint(3), myfloat(3.5543)))}func Join(sep string, parts ...fmt.Stringer) string {stringParts := make([]string, len(parts))for i, part := range parts {stringParts[i] = part.String()}return strings.Join(stringParts, sep)}
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