How to use the @available attribute in Swift

With Swift, we have the possibility to add attributes to our code to give the compiler more information.

One of those attributes is @available which we can use to make our code only available for certain Swift language versions or platforms.

Let's take a look at how to do that.

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Attributes in Swift

In general, an attribute in Swift is always specified with the @ symbol followed by the attribute's name and optionally its arguments enclosed in parentheses:

@name
@name(arguments)

The @available attribute

The @available attribute always has two or more arguments, separated by a comma, for example:

@available(*, unavailable, renamed: "updateCategories")
func update() {
}

In the above example, we declare the update method as not available on any platform because it was renamed to updateCategories.

Calling the update method will now fail with a compiler error:

update() has been renamed to updateCategories()

Arguments of @available attribute

Let's look at each argument we saw in the example in more detail.

The first argument is always a platform or language name, for example iOS, iOSApplicationExtension, swift. Alternatively, we can use an asterisk * to indicate that the availability applies to all platforms.

The remaining arguments can appear in any order:

• unavailable - to indicate that a declaration isn't available on the specified platform
• introduced: <version number> - to specify the first version in which a declaration was introduced
• deprecated: <version number> - to specify the first version when a declaration was deprecated
• obsoleted: <version number> - to specify the first version when a declaration was obsoleted and can no longer be used
• message: <message> - to provide a message for the compiler to display when emitting a warning or error
• renamed: <new name> - to provide a new name

The <version number> consists of one to three positive integers separated by periods, for example:

@available(iOS, introduced: 15.1)
struct Content {
}

Combination of @available attributes

We can combine multiple availability declarations as follows:

@available(swift, introduced: 4.0.2)
@available(iOS, introduced: 15.1.1)
struct Content {
}

Shorthand syntax

In case that only an introduced argument is used like we saw in the example above, we have the possibility to use a shorthand syntax as follows:

@available(swift 4.0.2)
@available(iOS 15.1.1, *)
struct Content {
}

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