xesite/blog/the-blind-men-and-the-animal-interface-2018-12-12.markdown

---
title: The Blind Men and The Animal Interface
date: 2018-12-12
---

A group of blind men heard that a strange animal had been brought to the town function, but none of them were aware of its type.

```
package blindmen

type Animal interface{
  error
}

func Town(strangeAnimal Animal) {
```

Out of curiosity, they said: “We must inspect and know it by type switches and touch, of which we are capable”.

```
type Toucher interface {
  Touch() interface{}
}
```

So, they sought it out, and when they found it they groped about it.

```
for man := range make([]struct{}, 6) {
   go grope(man, strangeAnimal.(Toucher).Touch())
}
```

In the case of the first person, whose hand landed on the trunk, said “This being is like a thick snake”.

```
type Snaker interface {
  Snake()
}

func grope(id int, thing interface{}) {
  switch thing.(type) {
  case Snaker:
    log.Printf("man %d: this thing is like a thick snake", id)
```

For another one whose hand reached its ear, it seemed like a kind of fan.

```
type Fanner interface {
  Fan()
}

// in grope switch block
case Fanner:
  log.Printf("man %d: this thing is like a kind of fan", id)
```

As for another person, whose hand was upon its leg, said, the it is a pillar like a tree-trunk.

```
type TreeTrunker interface {
  TreeTrunk()
}

// in grope switch block
case TreeTrunker:
  log.Printf("man %d: this thing is like a tree trunk", id)
```

The blind man who placed his hand upon its side said, “it is a wall”.

```
type Waller interface {
  Wall()
}

// in grope switch block
case Waller:
  log.Printf("man %d: this thing is like a wall", id)
```

Another who felt its tail, described it as a rope.

```
type Roper interface {
  Rope()
}

// in grope switch block
case Roper:
  log.Printf("man %d: this thing is like a rope", id)
```

The last felt its tusk, stating the thing is that which is hard, smooth and like a spear.

```
type Tusker interface {
  Tusk()
}

// in grope switch block
case Tusker:
  log.Printf("man %d: this thing is hard, smooth and like a spear", id)
```

All of the men spoke fact about the thing, but none of them spoke the truth of what it was.

```
// after grope switch block
log.Printf("%T", thing) // prints Elephant
```

---

```
  switch thing.(type) {
  case Trunker:
    log.Printf("man %d: this thing is like a thick snake", id)
  case Fanner:
    log.Printf("man %d: this thing is like a kind of fan", id)
  case TreeTrunker:
    log.Printf("man %d: this thing is like a tree trunk", id)
  case Waller:
    log.Printf("man %d: this thing is like a wall", id)
  case Roper:
    log.Printf("man %d: this thing is like a rope", id)
  case Tusker:
    log.Printf("man %d: this thing is hard, smooth and like a spear", id)
  }
```

---

Much later, after the other men had left the animal, a final blind man came over and looked the elephant right in the eye. He took a moment to compose himself, dusted his cloak off and spoke: "Hello. I am a blind man. I cannot see, but I would like to learn more about you and what it's like to be you. Who are you and what is it like? How does that help you? Also, I don't mean to be imposing, but how can I help you?"

The elephant started to hug his new friend, the blind man, close to him, crying with tears of joy. This blind man could see what the other blind men did not, even though he was blind.

---

[Alternate Ending](https://write.as/7mrvks0tq3jnpfoe.md)