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iOS

Posted by Kevin Her
Kevin Her
7,220 Points

What is the the difference between assigning an empty value to a variable versus variable with just type annotation?

What is the the difference between assigning an empty value to a variable versus variable with just type annotation in swift 2.

Here is an example of my code: How come the top one works in comparison with the bottom one?

let hourOfDay = 12
let timeOfDay: String

if hourOfDay < 6 {
    timeOfDay = "Early Morning"
} else if hourOfDay < 12 {
    timeOfDay = "Morning"
} else if hourOfDay < 17 {
    timeOfDay = "Afternoon"
} else if hourOfDay < 20 {
    timeOfDay = "Evening"
} else if hourOfDay < 24 {
    timeOfDay = "Late Evening"
} else {
    timeOfDay = "INVALID HOUR!"
}
______________________________
let hourOfDay = 12
let timeOfDay = ""

if hourOfDay < 6 {
    timeOfDay = "Early Morning"
} else if hourOfDay < 12 {
    timeOfDay = "Morning"
} else if hourOfDay < 17 {
    timeOfDay = "Afternoon"
} else if hourOfDay < 20 {
    timeOfDay = "Evening"
} else if hourOfDay < 24 {
    timeOfDay = "Late Evening"
} else {
    timeOfDay = "INVALID HOUR!"
}

1 Answer

Jason Anders
MOD
Jason Anders
Treehouse Moderator 145,863 Points
Jason Anders
Jason Anders
Treehouse Moderator 145,863 Points

Hey Kevin,

It has to do with using let as opposed to var.

In your first code block, you have declared a constant called timeOfDay to be a string, but it is not initialized. So, as you know, when you use let, the value cannot be changed. But, because you only declared it and didn't initialize it, there is no value, so you aren't changing anything. When your if/else block runs, it is assigning (or initializing) timeOfDay for the first time.

In your second code block, you are declaring and initializing timeOfDay with an empty string. Swift doesn't care if the string is empty or not, it only cares that something (in this case the empty string) was assigned (initialized) to the constant. And, because they cannot be changed, the if/else block cannot assign the new value to it.

I hope that makes sense and helps to clear it up for you. Keep Coding! :dizzy:

Kevin Her
Kevin Her
7,220 Points

Jason,

Thank you for your time and knowledge. I spent the last couple hours trying to figure it out and it usually is the simplest of mistake I often overlook.