Is there a way to declare an inline function in Swift?

Question

I'm very new to the Swift language.

I wanted to declare an inline function just like in C++ so my func declaration looks like this:

func MyFunction(param: Int) -> Int {     ... } 

and I want to do something like this:

inline func MyFunction(param: Int) -> Int {     ... } 

I tried to search on the web but I didn't find anything relevant maybe there is no inline keyword but maybe there is another way to inline the function in Swift.

Answer 1

Swift 1.2 will include the @inline attribute, with never and __always as parameters. For more info, see here.

As stated before, you rarely need to declare a function explicitly as @inline(__always) because Swift is fairly smart as to when to inline a function. Not having a function inlined, however, can be necessary in some code.

Edit: Swift 5 added the @inlinable attribute. Make sure you read up about it, as there may be a couple of gotchas that might make in unusable. It's also only for functions/methods declared public, so it's meant for those wanting to expose inline stuff for those that link to your library.

Answer 2

All credit to the answer, just summarizing the information from the link.

To make a function inline just add @inline(__always) before the function:

@inline(__always) func myFunction() {  } 

However, it's worth considering and learning about the different possibilities. There are three possible ways to inline:

• sometimes - will make sure to sometimes inline the function. This is the default behavior, you don't have to do anything! Swift compiler might automatically inline functions as an optimization.
• always - will make sure to always inline the function. Achieve this behavior by adding @inline(__always) before the function. Use "if your function is rather small and you would prefer your app ran faster."
• never - will make sure to never inline the function. This can be achieved by adding @inline(never) before the function. Use "if your function is quite long and you want to avoid increasing your code segment size."