Swift notes operator _swift

Null-value merge operators and interval operators

The main things to see today are the basic operators in Swift. Record it.

Nil coalescing Operator

A?? b in the?? is a null-value merge operator that will judge a and, if not nil, unpack, or return B.

var a:string? = "a"
var b:string = "B"
var c = A?? b   //"a"
a = nil
c = a?? b     //"B"
B = nil
C = A ?? B?? "C"  //"C"

The following two points are required when used:

A must be optional.
b must be consistent with type a
In other words, a must have the possibility of being spare, B must have the qualification to prepare the tire.

In fact, a shorthand for the three-mesh operator:

Copy Code code as follows:

A!= nil? A! : b or a = = nil? b:a!

Of course, you can also use custom operators to:

Infix operator | | | {} Func | | |

<T> (Left:t, right:t)-> T {
  if let L = left {return 
    L} return right
}

var a:string?
var b = "B"
var c = a | | | b

There is also a in C #?? , interested can go to understand.

Range Operator

The interval operators are divided into closed intervals (...) and left-right open intervals (...). <) Two, the former is to calculate the end of the head, the latter is not the end of the calculation.

can be applied in switch:

Switch anumber
{case
0...5:
  println (' This # is between 0 and 5 ') Case
6...10:
  println (" This is between 6 and ten ")
Default: println (" This number is not
  between 0 ")
}

The interval operator actually returns a Range<t> object and is a collection of sequential indexes with no associated sequence.

Say, left and right. , which is exactly the opposite of Ruby's ...

But someone just wants to use. , then you can write one yourself:

Infix operator. {associativity None precedence 135}

Func.. (Lhs:int, Rhs:int)-> range<int> {return
  LHS ... <RHS
} for

I in 0..10 {
  println ("Index \ (i)")
}

You can also use Generate () to traverse:

var range = 1...4
var generator = range.generate ()  //{StartIndex 1, endindex 5}
Generator.next ()//1
Generator.next ()//2
Generator.next ()//3
Generator.next ()//4
Generator.next ()//Nil

. Generate () returns a rangegenerator<t> structure that can be used to traverse the values in range<t>.

There used to be a (5...1). by (-1) usage, but it seems useless now.

The interval operator returns a closedinterval or Halfopeninterval thing, and the type is just comparable. So we can also put String into ... In

For example, Cat God's swifter tips in a chapter of the code below, through a string of closedinterval to output the lowercase letters in the string:

Let test = "Hello" let
interval = "a" ... "Z" for

C in test {
  if Interval.contains (String (c)) {
    println ("\" C )")
  }
}

SubString

Ruby is handy for using dots to get SubString:

2.1.3:001 > a= "abc"
 => "abc"
2.1.3:002 > A[0]
 => "a"
2.1.3:003 > a[0..1]
 => "AB"

And there is no subscript in Swift's closedinterval. But the wayward we are to use [1...3] This method how to do?
own hands and clothing, write a extension bar, only need to add a subscript on it, and then the type of subscript is range<int> can be:

Extension string {
  subscript (r:range<int>)-> string {Get
    {let
      startIndex = Advance (self.startin Dex, R.startindex) let
      endindex = Advance (StartIndex, R.endindex-r.startindex) return

      self[range (start: StartIndex, End:endindex)]}}

var s = "Hello, playground"

println (s[0...5])//==> "Hello,"
println (s[0..<5])//==> "Hello"

If you want to search for a target string and then intercept substring, you can do this:

Let-name = "Joris kluivers" let

-start = Name.startindex let
-end = Find (name, "")

if (end!= nil) {
  Le T firstName = Name[start. <end!]
} else {
  //No space found
}

The above mentioned is the entire content of this article, I hope you can enjoy.