Detailed explanation of swift where and matching pattern instance

Detailed explanation of swift where and matching pattern instance

Preface:

Among the new features provided by Swift to Objective-C programmers, there is a feature that disguises itself as a boring old man, but it has great potential in how to elegantly solve the problem of "the pyramid of whip corpse". Obviously, the feature I'm talking about is the switch statement. For many Objective-C programmers, except for being more interesting on Duff's Device, the switch statement is very clumsy and has almost no advantage over multiple if statements.

1. Basic use

Swift can use where to restrict the conditions after the switch statement case

let point = (3,3)
switch point{
case let (x,y) where x == y:
  print("It's on the line x == y!")
case let (x,y) where x == -y:
  print("It's on the line x == -y!")
case let (x,y):
  print("It's just an ordinary point.")
  print("The point is ( \(x) , \(y) )")
}

2. How to use if - case - where statement instead of switch statement

let age = 19
switch age{
case 10...19:
  print("You're a teenager.")
default:
  print("You're not a teenager.")
}


if case 10...19 = age{
  print("You're a teenager.")
}

if case 10...19 = age where age >= 18{
  print("You're a teenager and in a college!")
}

Note: the case condition must be placed before "="

After swift 3.0, if case after "where" is used instead of ""

3. Use if-case in combination with tuples (use tuple unpacking)

let vector = (4,0)
if case ( let x , 0 ) = vector where x > 2 && x < 5{
  print("It's the vector!")
}

4. case - where combined with loop

for i in 1...100{
  if i%3 == 0{
    print(i)
  }
}

for case let i in 1...100 where i % 3 == 0{
  print(i)
}

Using case restrictions can greatly reduce the amount of code, which is very convenient to use. It is a major feature of the swift language. If you master it well, you can write beautiful and concise code.

Thank you for reading, I hope it can help you. Thank you for your support for this site!