Go Golang：自定义类型上的类型断言

I am practicing sort using heap but

  prog.go:85: type bucket is not an expression
  prog.go:105: cannot use heap.Pop(bucket[i].([]IntArr)) (type interface {}) as type int in assignment: need type assertion
  [process exited with non-zero status]

I am getting those errors and can't figure out how to type assert properly

The problem is from the lines:

  heap.Push(bucket[x].([]IntArr), elem)

  arr[index] = heap.Pop(bucket[i].([]IntArr))

Because I want to use heap structure in order to extract values from each bucket

[]IntArr

IntArr[]int

type IntArr []int
type bucket [10]IntArr

I have been trying many ways over the weekend and can't figure out, I greatly appreciate it.