Swift foundation features unique to swift

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Preface

This article introduces swift relative oc,swift Unique usage , In combination with the requirements in development

On the subject

internal

internal Property usage for

internal Decorated attributes , There is always only one object address , It's like a single case

class Service {
    internal static let name = "fenghanxu"
}

controller A Use attributes

controller B Use attributes

Print the results

A controller , The attribute address is : 0xb21b7768d2b563c4
B controller , The attribute address is : 0xb21b7768d2b563c4
A controller , The attribute address is : 0xb21b7768d2b563c4

throws

When we use the system method, we often see that the system has a writing method throws Property to modify the method . for example ： Look at the picture below .

If the method is useful throws Embellished words , You need to throw an exception when using the method .

There are two common ways to use this method ：

Usage mode 1：

Usage mode 2：

guard

stay swift In development guard It's very common , General usage , for example ：A Property does not confirm whether there is a value , But we need to use A Value , If A You can't go on without them . So you need to use guard Yes A Unpack to see if there is value , For example, look at the following code .

because num_0 Do not confirm whether there is a value =, So you need to unpack before using

The second is to use guard The most common use is in closures .

Explain why to self Unpacking , Because after the closure comes back, the current self I don't know if it still exists , If you are released, you will not be able to self The properties in the , So it's using self Before the properties of self Unpacking , If there is self Just go down . Quit without .

If it is not unpacked for use self Will bring question mark (?) for example ： Look at the code below

(?) Use of question marks

What situation attribute is followed by a question mark . This is a little bit easier

For example, the picture above , If tableview When it is created, it is created like the following image form , When you use it, you will tableview Followed by a question mark . Because when using this object , I don't know if it has become a powerful object , If not, do not set related properties , Only if the strength is changed .

So what is the general requirement to use the above image to create attributes .
In a controller , You need to pop up a box , This box is only created when it needs to be used , If you create attributes in the form of the above picture , The box will be removed when you run out of it .

(??) Use of double question marks

As can be seen from the picture above , We are going to put height Assign a value to an object statusBarHeight, however height It's from statusBarManager Objects are taken out , however statusBarManager I don't know if it exists , If it doesn't exist ,height There is no such thing as , however statusBarHeight Confirm that you need to get a value . So when you use a value, you need to bring a Double question mark , If height If you don't get the value, you will get the default value after the double question mark .