What input will cause golang's json.Marshal to return an error?

Question

From the docs:

JSON cannot represent cyclic data structures and Marshal does not handle them. Passing cyclic structures to Marshal will result in an i

Answer 1

Update: now using a channel instead of a map[int]int to elicit the error

---

Go-specific structures,e.g. func or chan refuse to serialize:

package main

import (
    "encoding/json"
    "fmt"
)

func main() {
    value := make(chan int)
    _, err := json.Marshal(value)
    fmt.Println(err)
}