I don't understand why we have "let descprition" inside the parentheses

Hello Ken,

Enums have associated values, that you can "extract" their value by creating a constant.

For example,

Consider the following Enum

// An enum that can store associated values 

enum WeekDays {
    case monday(String)
    case tuesday(String)
    case wednesday(String)
    case thursday(String)
    case friday(String)
}

We can now create an instance of the WeekDays enum with an associated value.

let weekDay = WeekDays.monday("Not my favorite day") // Assigning a value to its associated value

Now we can use a switch statement to "switch" through it, and extract the value by initializing a constant.

switch weekDay {
case .monday(let value) : // Extracting the value by initializing a constant
    print(value) // Prints : Not my favorite day
case .tuesday(let value) :
    print(value)
default:
    break
}

// Or you can also do it this way

switch weekDay {
case let .monday(value)  :
    print(value)
case let .tuesday(value) :
    print(value)
default:
    break
}

This is essentially what Pasan is doing in his video with the Error handling. Notice how he uses an enum to define errors, and these errors have an associated value, then he is extracting it's value if the error is thrown.

For more information about this you should look at Enums and associated values.

Click here to see more about enums.

Hope this helps