Check for nil with guard instead of if?

Question

Is there a guard equivalent of checking if a variable is nil? If so how would I translate a statement like this to use guard instead?

if post["preview"]! != nil {     //do stuff } else {     //handle case where the variable is nil } 

Answer 1

Like some people already answered, you can use let

guard let preview = post["preview"] else { /* Handle nil case */ return } 

If you are not using the variable, you can use an underscore to not declare the variable and avoid the warning.

guard let _ = post["preview"] else { /* Handle nil case */ return } 

You can also do a regular boolean check instead of using let

guard post["preview"] != nil else { /* Handle nil case */ return } 

A more general case for a boolean check on a guard

guard conditionYouExpectToBeTrue else { /* Handle nil case */ return } 

If you want to be able to modify the variable, you can use var instead of let

guard var preview = post["preview"] else { /* Handle nil case */ return } 

Swift 3.0

You can combine var/let with a boolean check by using commas between the statements.

guard let preview = post["preview"], preview != "No Preview" else { /* Handle nil case */ return } 

Swift 2.x

You can combine var/let with the boolean check by using where where

guard let preview = post["preview"] where preview != "No Preview" else { /* Handle nil case */ return } 

Answer 2

You can use guard to grab the value from the post dictionary:

guard let value = post["preview"] else {     return  // or break, or throw, or fatalError, etc. } // continue using `value`