This tutorial belongs to the Swift series

A comment in Swift can take 2 forms: a single-line comment, and a multi-line comment.

A single-line comment is

//this is a comment

and it can be put at the end of a line of code:

let a = 1 //this is a comment

A multi-line comment is written using this syntax:

/* this
 is
    a multi-line
 comment
*/

Swift allows to nest multi-line comments:

/* this
 is
    a /* nested */ multi-line
 comment
*/

which is handy especially when commenting out large portions of code that already contains multi-line comments.