Guard Clauses

Here is an example of guard clauses from the notes:

• Guard clauses are at the start of a function before the main processing
• The main processing, the reason you are writing the function, comes at the end
• Experienced developers scan past the guard clauses when they are interested in the main processing, so the fact they are first does not matter
• The main processing here was simple, but it may not be and typically isn't
• The main processing should not be in an if-statement for something that can be in a guard clause
• Repeating the main processing is not a good option

The previous example is standard but not very good. Let's see another one:

• Never lose applicable comments when refactoring or performing any development
• Put comments on the line before what they describe, not at the EOL
• Guard classes contain a return or throw

Swift Guard Statement

The Swift language has a guard statement:

If the condition is true, processing after the guard statement continues. If the condition is false, then the else is executed. Note that the else must contain a return or throw. The scope of the variable extends outside of the guard statement and is in scope throughout the rest of the block the guard statement is in.

The guard statement was added in Swift 2.0. A more typical usage is declaring variables with the let statement that are optionals (which map nicely to nullable pointers):

where the Swift language class DataManager maps to this Objective-C:

Note that Objective-C is a superset of the C language, so it has pointers. NSString is the standard string class.

Before Swift 2.0, without the _guard statement*, it required you to:

This is even more noticeable when there are multiple levels of optionals:

This was why Swift 2.0 added the guard statement: