[Swift] Implement new Concept Exercise: functions

[wneumann]

This issue describes how to implement the functions concept exercise for the Swift track.

Getting started

Please please please read the docs before starting. Posting PRs without reading these docs will be a lot more frustrating for you during the review cycle, and exhaust Exercism's maintainers' time. So, before diving into the implementation, please read the following documents:

• The features of v3.
• Rationale for v3.
• What are concept exercises and how are they structured?

Please also watch the following video:

• The Anatomy of a Concept Exercise.

Goal

This concept exercise should convey a basic understanding of how to work with functions in Swift.

Things to teach

• Function definition syntax
• Parameter labels and names
• Multiple function return values
• Default parameters
• Variadic parameters
• In-Out parameters
• Nested functions

Things not to teach

• Closures
• Higher-order functions

Concepts

• multiple-return-values
• default-parameters
• variadic-parameters
• inout-parameters
• nested-functions

Prerequisites

• basics
• tuples

Resources to refer to

Hints

• Functions

After

• Functions

Representer

TBD

Analyzer

TBD

Implementing

See the Swift track implementation guide for guidance.

Help

If you have any questions while implementing the exercise, please post the questions as comments in this issue.

[wneumann]

Note that this will need to come before many others in the progression where the stories make more sense using inout functions. It should probably lie between basics and most other exercises.

[wneumann]

PR added. Awaiting review.

[wneumann]

Closed with PR https://github.com/exercism/v3/pull/2005