"Swift" Learning Notes (eight)--classes and structs

1. Definitions of classes and structures

<pre name= "code" class= "HTML" >struct Resolution {    var width = 0    var height = 0}class Videomode {    var res Olution = Resolution ()    var interlaced = False    var framerate = 0.0    var name:string?    The value is an optional string type name}

Class: Keyword class, struct: struct

2. Create instances of classes and structs (other languages are called instances as objects.) )

Let someresolution = Resolution () Let Somevideomode = Videomode ()

Gee, very simple ah, how not the keyword new .... and assigning a function to a variable is the same. Yes. It's so simple. No keywords required.

3, the structure has a property-by-attribute constructor, class wood has.

Let VGA = Resolution (width:640, height:480)

4, use. Points to access properties, including access and assignment.

SomeVideoMode.resolution.width = 1280

5, the struct is a value type, and the class is a reference type.

6. The identity operator of the class is equivalent to (= = =), not equivalent to (!==) determining whether two variables or constants refer to the same instance

7, the pointer does not need a specific (*) to indicate is a memory address reference, and do not need a specific symbol (-) to access, it is the same as the Access property (.) Point.

8. Differences between classes and structures

Classes and structs in Swift have a lot in common. The Common place is:

• Defining properties for storing values
• Define methods to provide functionality
• Defining satellite scripts for accessing values
• Defining constructors for generating initialization values
• Extended to add functionality to the default implementation
• Compliance with protocols to provide standard functionality for a class

Compared to structs, classes have the following additional functions:

• Inheritance allows one class to inherit the characteristics of another class
• Type conversions allow you to check and interpret the type of a class instance at run time
• The destructor allows an instance of a class to release any resources it has been assigned
• Reference count allows multiple references to a class

9. Selection of classes and structures

As a general guideline, consider building a struct when one or more of the following conditions are met:

• The main purpose of the structure is to encapsulate a small number of related simple data values.
• It is reasonable to expect that when an instance of a struct is assigned or passed, the encapsulated data will be copied instead of referenced.
• Any value type attribute stored in the struct will also be copied, not referenced.
• Structs do not need to inherit the properties or behaviors of another existing type.

Suitable structural candidates include:

• The size of the geometry, encapsulating an width attribute and a height property, both Double types.
• A path within a range that encapsulates a start property and length attribute, both of which are Int types.
• In a three-dimensional coordinate system, a point, package x , y and z attribute, all of them are Double types.

In all other cases, define a class, generate an instance of it, and manage and pass it by reference. In practice, this means that the vast majority of custom data constructs should be classes, not structs.

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"Swift" Learning Notes (eight)--classes and structs