You're right. But it will return something: https://go.dev/play/p/Cz6aeGpURgo

  my_map := make(map[int32][]int64)
  val := my_map[123]
  val = append(val, 456)
  my_map[123] = val
  fmt.Println(my_map)

prints `map[123:[456]]`

I guess it's convenient compared to Rust's strict approach with entry API. But also, what I found is that golang's subscript returns nil in one case: if the value type is a nested map.

  my_map := make(map[int32]map[int32]int64)
  val := my_map[123]
  val[456] = 789
  my_map[123] = val
  fmt.Println(my_map)

output:

  panic: assignment to entry in nil map