It’s possible to modify the properties of a struct, but only if that struct is created as a variable. Of course, inside your struct there’s no way of telling whether you’ll be working with a variable struct or a constant struct, so Swift has a simple solution: any time a struct’s method tries to change any properties, you must mark it as
You don’t need to do anything else other than mark the method as
mutating, but doing that gives Swift enough information to stop that method from being used with constant struct instances.
There are two important details you’ll find useful:
mutatingwill stop the method from being called on constant structs, even if the method itself doesn’t actually change any properties. If you say it changes stuff, Swift believes you!
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