Refactoring

---

## 1. Updating an existing program

## 2. Creating one from scratch
]

---
# New application

## 2. Understand the business requirements

## 3. No users!
]

---
# Existing application

## 2. Limited test coverage

## 3. Original developers and business      users have left the organization
]

---
class: medium-code

# Refactoring: reorder variables

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = funA(user)
  val res2 = funB(user)
  // ...
}
```
]

---
class: medium-code

# Refactoring: reorder variables

.forty-seven-left[
```scala
def helloV1(`user: User`) = {
  val res1 = funA(user)
  val res2 = funB(user)
  // ...
}
```
]

---
class: medium-code

# Refactoring: reorder variables

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = `funA(user)`
  val res2 = `funB(user)`
  // ...
}
```
]

---
class: medium-code

# Refactoring: reorder variables

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val `res1` = funA(user)
  val `res2` = funB(user)
  // ...
}
```
]

---
class: medium-code

# Refactoring: reorder variables

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = funA(user)
  val res2 = funB(user)
  // `...`
}
```
]

---
class: medium-code

# Refactoring: reorder variables

.forty-seven-left[
```scala
def helloV1(user: User) = {
  `val res1 = funA(user)`
  val res2 = funB(user)
  // ...
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) = {
  val res2 = funB(user)
  `val res1 = funA(user)`
  // ...
}
```
]

---
class: medium-code

# Refactoring: reorder variables

.forty-seven-left[
```scala
def helloV1(user: User) = {
  `val res1 = 10`
  val res2 = ""
  // ...
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) = {
  val res2 = ""
  `val res1 = 10`
  // ...
}
```
]

---
class: medium-code

# Refactoring: reorder variables

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = db.delete(user.id)
  val res2 = db.insert(user)
  // ...
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) = {
  val res2 = db.insert(user)
  val res1 = db.delete(user.id)
  // ...
}
```
]

.forty-seven-right[
```scala
helloV1(user) // user saved in db
helloV2(user) // user deleted from db
```
]

---
class: medium-code

# Refactoring: remove unused code

.forty-seven-left[
```scala
def helloV1(user: User) = {
  funA(user)
  val res1 = funB(user)
  val res2 = funC(user)
  res1
}
```
]

---
class: medium-code

# Refactoring: remove unused code

.forty-seven-left[
```scala
def helloV1(user: User) = {
  `funA(user)`
  val res1 = funB(user)
  val res2 = funC(user)
  res1
}
```
]

---
class: medium-code

# Refactoring: remove unused code

.forty-seven-left[
```scala
def helloV1(user: User) = {
  funA(user)
  `val res1 = funB(user)`
  `val res2 = funC(user)`
  res1
}
```
]

---
class: medium-code

# Refactoring: remove unused code

.forty-seven-left[
```scala
def helloV1(user: User) = {
  funA(user)
  val res1 = funB(user)
  val res2 = funC(user)
  `res1`
}
```
]

---
class: medium-code

# Refactoring: remove unused code

.forty-seven-left[
```scala
def helloV1(user: User) = {
  funA(user)
  val res1 = funB(user)
  val `res2` = funC(user)
  res1
}
```
]

---
class: medium-code

# Refactoring: remove unused code

.forty-seven-left[
```scala
def helloV1(user: User) = {
  `funA(user)`
  val res1 = funB(user)
  `val res2 = funC(user)`
  res1
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) =
  funB(user)
```
]

---
class: medium-code

# Refactoring: remove unused code

.forty-seven-left[
```scala
def helloV1(user: User) = {
  funA(user)
  val res1 = funB(user)
  val res2 = funC(user)
  res1
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) =
  funB(user)
```
]

---
class: medium-code

# Refactoring: remove unused code

.sixty-two-left[
```scala
def helloV1(user: User) = {
  if(user.email.isEmpty) throw new InvalidUser("No email")
  val res1 = funB(user)
  val res2 = sendEmail(user)
  res1
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) =
  funB(user)
```
]

---
class: medium-code

# Refactoring: remove unused code

.sixty-two-left[
```scala
def helloV1(user: User) = {
  `if(user.email.isEmpty) throw new InvalidUser("No email")`
  val res1 = funB(user)
  val res2 = sendEmail(user)
  res1
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) =
  funB(user)
```
]

---
class: medium-code

# Refactoring: remove unused code

.sixty-two-left[
```scala
def helloV1(user: User) = {
  if(user.email.isEmpty) throw new InvalidUser("No email")
  val res1 = funB(user)
  val res2 = `sendEmail(user)`
  res1
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) =
  funB(user)
```
]

---
class: medium-code

# Refactoring: de-duplicate

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = funA(user)
  // ..
  val res2 = funA(user)
  funB(res1, res2)
}
```
]

---
class: medium-code

# Refactoring: de-duplicate

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = `funA(user)`
  // ..
  val res2 = `funA(user)`
  funB(res1, res2)
}
```
]

---
class: medium-code

# Refactoring: de-duplicate

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = funA(user)
  // ..
  val res2 = funA(user)
  funB(res1, `res2`)
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) = {
  val res1 = funA(user)
  // ..
  funB(res1, `res1`)
}
```
]

---
class: medium-code

# Refactoring: de-duplicate

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = funA(user)
  // ..
  val res2 = funA(user)
  funB(res1, res2)
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) = {
  val res1 = funA(user)
  // ..
  funB(res1, res1)
}
```
]

---
class: medium-code

# Refactoring: de-duplicate

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = funA(user)
  // ..
  val res2 = funA(user)
  funB(res1, res2)
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) = {
  val res1 = funA(user)
  // ..
  funB(res1, res1)
}
```
]

.forty-seven-right[
```scala
def funA(user: User): BlogPost =
  BlogPost(
    id        = `UUID.randomUUID()`,
    author    = user.name,
    content   = "",
    createdAt = `Instant.now()`,
  )
```
]

---
class: medium-code

# Refactoring: de-duplicate

.forty-seven-left[
```scala
def helloV1(user: User) = {
  val res1 = funA(user)
  // ..
  val res2 = funA(user)
  funB(res1, res2)
}
```

### Is helloV1 equivalent to helloV2?

```scala
def helloV2(user: User) = {
  val res1 = funA(user)
  // ..
  funB(res1, res1)
}
```
]

helloV1(user) // charge `$200`
helloV2(user) // charge `$100`
```
]

---
class: medium-code