Does the Swift compiler ignore unused functions?

Question

Does the Swift compiler compile unused functions or does it ignore them?

Answer 1

Unused functions do make your program larger.

This is pretty easy to test. Created a new Swift application as a Single View Application (iOS). In the generated ViewController.swift, add a function. Do a build (Command-B) and check the product's build folder. This is usually:

~/Library/Developer/Xcode/DerivedData/
    <AppName>-<IDString>/Build/Products/Debug-iphoneos/
    <AppName>.app/

Check the file size of <AppName>.

Comment out the function and do a build again. The file size will be smaller.

I created an app called SwiftSandbox and added this:

func doSomething() -> NSString {
    var v: NSMutableString = NSMutableString(string: "MyString is Funny")
    v.replaceCharactersInRange(NSMakeRange(3, 3), withString: "World")
    return v
}

When building with this function, I saw this in bash:

-rwxr-xr-x   1 test  staff  213648 Apr 27 11:33 SwiftSandbox*

With the function commented out:

-rwxr-xr-x   1 test  staff  142992 Apr 27 11:33 SwiftSandbox*

Note that I didn't change any optimization settings in Xcode so I can't be sure what effect that would have.