CODEWITHSUNDEEP
goreflectionslicego-reflect
Mojito
Mojito

Reputation: 27

How to get the element type of slice?

If there is a struct like:

type A struct {
  Arr []int
}

How can I get the element type in the slice arr?

for example, an empty A instance is passed in, how can I get the int type?

func PrintElementType(obj interface{}) {
    objType := reflect.TypeOf(obj)
    for i := 0; i < objType.NumField(); i++ {
        fieldType := objType.Field(i).Type
        // here I got 'slice'
        fmt.Println(fieldType.Kind())
        // here I got '[]int', I think 'int' type is stored somewhere...
        fmt.Println(fieldType)
        // so, is there any way to get 'int' type?
        fmt.Println("inner element type?")
    }
}

func main() {
    a := A{}
    PrintElementType(a)
}

Upvotes: 1

Views: 463

Answers (1)

icza
icza

Reputation: 417512

If you have the reflect.Type type descriptor of a slice type, use its Type.Elem() method to get the type descriptor of the slice's element type:

fmt.Println(fieldType.Elem())

Type.Elem() may also be used to get the element type if the type's Kind is Array, Chan, Map, Ptr, or Slice, but it panics otherwise. So you should check the kind before calling it:

if fieldType.Kind() == reflect.Slice {
    fmt.Println("Slice's element type:", fieldType.Elem())
}

This will output (try it on the Go Playground):

slice
[]int
Slice's element type: int

Upvotes: 2

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