douxiong2738 2018-08-27 18:23
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获取未知类型的切片的长度

Let's say I have a function that returns an interface{}. But I know that item returns is a slice of some kind. How can I determine the length of that slice? Here's sample code of what I tried, but they all cause compilation error.

package main

import (
  "log"
  "reflect"
)
func SomeKindOfSlice() interface{} {
  return []int64{0,1,2,3,4,5,6,7,8,9}
}
func main() {
  slice := SomeKindOfSlice()
  /*log.Println(reflect.TypeOf(slice).Len())
  log.Println(reflect.TypeOf(slice).Type().Len())
  log.Println(reflect.ValueOf(slice).Type().Len())
  log.Println(reflect.ValueOf(slice).Elem().Type().Len())
  */
  log.Println(reflect.ValueOf(slice).Elem().Type().Len())
}

I'd like to avoid the brute force way of specifically type asserting the slice variable just to find the length.

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1条回答 默认 最新

  • dqdl6469 2018-08-27 18:31
    关注

    In your current attempt of the refect package usage you are querying for the Len of the Type. So this assumes you are dealing with an array not a slice. The difference being that a array is a fixed size slice, a slice has unbound length.

    Check this code for demonstration

    package main
    
    import (
      "log"
      "reflect"
    )
    func SomeKindOfSlice() interface{} {
      return []int64{0,1,2,3,4,5,6,7,8,9}
    }
    func SomeKindOfArray() interface{} {
      return [10]int64{0,1,2,3,4,5,6,7,8,9}
    }
    func main() {
      log.Println(reflect.ValueOf(SomeKindOfSlice()).Len())
      log.Println(reflect.ValueOf(SomeKindOfArray()).Type().Len())
    }
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论

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