@ Available and # available in Swift,

@ Available and # available in Swift,

The availability concept is introduced in Swift 2.0. You can use functions, classes, protocols, etc.@availableDeclare that these types of lifecycles depend on specific platforms and operating system versions. While#availableIt is used in judgment statements (if, guard, while, etc.) to implement different logic on different platforms.

@ Available usage

@availablePut it in front of a function (method), class, or protocol. Indicates the platforms and operating systems applicable to these types. Let's look at the following example:

@available(iOS 9, *)func myMethod() {    // do something}

@available(iOS 9, *)Must contain at least 2 feature parameters, of whichiOS 9Indicates that it must be in iOS 9 or later versions. If your deployed platform includes iOS 8, the compiler reports an error after calling this method.
Another feature parameter: asterisk (*), indicating that all platforms are included. Currently, the following platforms are available:

• IOS
• IOSApplicationExtension
• OSX
• OSXApplicationExtension
• WatchOS
• WatchOSApplicationExtension
• TvOS
• TvOSApplicationExtension

Generally, if there are no special cases*Indicates the entire platform.

@available(iOS 9, *)Is a short form. The full write format is@available(iOS, introduced=9.0).introduced=9.0The parameter indicates that the Declaration is introduced from 9.0 on the specified platform (iOS. Why can I use the simplified form? When onlyintroducedSuch a parameter can be abbreviated to the preceding abbreviated form. Likewise: @ available (iOS 8.0, OSX 10.10, *) is also possible. It indicates the availability on multiple platforms (iOS 8.0 and above; OSX 10.10 and above) at the same time.

In addition,@availableOther parameters can be used:

• Deprecated = version number: Indicates that a specified platform version expires.
• Obsoleted = version number: Deprecated a specific version of the specified platform,deprecatedYes, you can continue using it, but it is not recommended,obsoletedIndicates that the call will cause compilation errors.) This statement
• Message = Information Content: Provide some additional information
• unavailable: The specified platform is invalid.
• Renamed = new name: Rename Declaration

For more information about the preceding parameters, see the official documentation.

# Available

# Available is used in the code block of conditional statements to determine different platforms and perform different logic processing, such as: if # available (iOS 8 ,*) {// run on iOS 8 and above} guard # available (iOS 8, *) else {return // return directly for systems below iOS 8}

Stackoverflow Problems

• Difference between @ available and # available in swift 2.0: @ available and # available
  The post also mentions a problem:@availableIs it determined during compilation? While#availableIs it a running behavior?