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Gregory Millan3,719 Points
Optional question from quiz
How is the following question's answer an optional and not an Int?
What is the data type of the constant today? let today = Day(rawValue: 1)
Steven Deutsch21,046 Points
Hey Gregory Millan,
In this example code, the type of the constant "today" will be Day?. Let me explain the reasoning behind this.
Take a look at the following code:
let today = Day(rawValue: 1)
We are initializing the value for today by using a raw value. This raw value will assign the enum member of Day that it corresponds to, to the constant today. However, its possible try and initialize a type of Day by using an invalid raw value. For example, if our enum only had 7 members - the 7 days in the week, and we tried to initialize with a raw value of 8, the raw value initialization would fail. This is what makes this method of initialization, from a raw value, known as a failable initializer and it is the reason why today is of type Day?. Initializing from a raw value ALWAYS returns an optional type whether it succeeds or fails, as a safety feature.
Hope this helps, good luck!
Jason AndersTreehouse Moderator 145,855 Points
This is returning an optional because it's not sure if the raw value exists. When you do that line of code, it is not returning the int that is passed in as the raw value, but rather the value that is assigned to the raw value. It has to return an optional in case the raw value passed in has not been assigned to a specific value.
Amit covers this in this video starting at the 6:00 mark. You may want to review this part of the video and how raw values work in Swift.