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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 } 
494
in other words, "guard let" is used when the code is 99% sure of not using the else conditional; in the other hand, "if let" when the code is 50 - 50(example) to use else condition. The variable bound by if let is only visible inside if let scope. The variable bound by guard let is visible afterwards.
In if let , the defined let variables are available within the scope of that if condition but not in else condition or even below that. In guard let , the defined let variables are not available in the else condition but after that, it's available throughout till the function ends or anything.
In Swift, we use the guard statement to transfer program control out of scope when certain conditions are not met. The guard statement is similar to the if statement with one major difference. The if statement runs when a certain condition is met. However, the guard statement runs when a certain condition is not met.
Swift gives us an alternative to if let called guard let , which also unwraps optionals if they contain a value, but works slightly differently: guard let is designed to exit the current function, loop, or condition if the check fails, so any values you unwrap using it will stay around after the check.
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 } 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` If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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