CODEWITHSUNDEEP
swift
Valentyn Zakharenko
Valentyn Zakharenko

Reputation: 3088

Is Foundation imported by default?

I have Cocoa Touch Framework. Each of all three following code samples as source of my Framework is successfully compilable.

import Foundation
protocol X {
    var a: Data { get }
}

protocol X {
    var a: Foundation.Data { get }
}

protocol X {
    var a: Data { get }
}

The last one uses type from Foundation without any importing of this module. Is Foundation imported by default into Swift file in case when module header (.h file) contains #import <UIKit/UIKit.h> (generated by default)?

Note (30.10.19)

I removed #import <UIKit/UIKit.h> and replaced FOUNDATION_EXPORT with extern in module header (.h file). After that I added import Foundation into my swift file. As a result only first example of code is compilable.

As I understand if module was imported into header (.h) of another module - it isn't necessary to import first module into Swift files of second module. Am I right?

Upvotes: 1

Views: 840

Answers (1)

MohyG
MohyG

Reputation: 1348

Yes UIKit imports Foundation so if you have #import <UIKit/UIKit.h> or import UIKit there is no need to import Foundation

Take a look at here in UIKit's source swift code Here

Edit

Here is useful information about how modules work in swift,

You can also selectively import certain declarations from a module:

import func Chess.createGreedyPlayer
import class Foundation.NSRegularExpression

Comparison with Other Languages

Importing a module is much like importing a library in Ruby, Python, or Perl, importing a class in Java, or including a header file in a C-family language. However, unlike C, module files are not textually included and must be valid programs on their own, and may not be in a textual format at all. Unlike Java, declarations in a module are not visible at all until imported. And unlike the dynamic languages mentioned, importing a module cannot automatically cause any code to be run.

Importing a module in swift uses one of three syntaxes below:

import [module]
import [module].[submodule]
import [import kind] [module].[symbol name]

when we do not specify the import kind while importing Data, we’re actually still just importing the entirety of Foundation.

there are multiple permissible import kinds available:

typealias | struct | class | enum | protocol | let | var | func

Like any other body of code, a module may depend on other modules in its implementation. The module implementer may also choose to re-export these modules, meaning that anyone who imports the first module will also have access to the declarations in the re-exported modules.

@exported import AmericanCheckers

As an example, the "Cocoa" framework on OS X exists only to re-export three other frameworks: AppKit, Foundation, and CoreData.

Just as certain declarations can be selectively imported from a module, so too can they be selectively re-exported, using the same syntax:

@exported import class AmericanCheckers.Board

Upvotes: 3

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