Swift 2.0 Study Notes (Day 27)--optional types

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Optional type:

Let's start by looking at the following code:

var Ten  = nil         // compile error  = nil    // Compile error

int and string types cannot accept nil, but sometimes it is unavoidable that the program is copied to nil during the run, and Swift provides an optional type (optional) for each data type, that is, a question mark (?) or exclamation point (!) after a data type. Modify the preceding example code:

var Ten  = nil let str:string! = Nil

int? and string! are both original type int and string optional types, they can accept nil.

Optional type value unpacking

What is the difference between a question mark (?) or an exclamation point (!) in an optional type? This is related to the "unpacking" (unwrapping) of the optional type, which is to turn the optional type into a normal type, and if we print a non-empty optional type value directly, the code is as follows:

var Ten Print (n1)

The result of the output is optional (10), not 10. So trying to evaluate the expression N1 + 100 will cause a compile error, the code is as follows:

var Ten  )      // Compile error occurred

It is necessary to "disassemble" the optional type value.

"Unpacking" is divided into show unpacking and hidden unpacking.

An optional type declared with a question mark (?) that requires an exclamation point (!) when unpacking, which is called an explicit unpacking;

An optional type declared with an exclamation point (!) that can be split without using an exclamation point (!), which is called an implicit unpacking.

Take a look at the following code:

 var  n1:int? = 10  print (N1 !) + 100 )  var  n2:int! = 100   print (N2  + 200 ) //  implicit unpacking  

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Swift 2.0 Study Notes (Day 27)--optional types