Why is this not adding my 2 variables together lol

# getting-started

[Sebastian]

Why is this not adding my 2 variables together lol

[FRQDO]

What's the return type of readLine() ?

[Sebastian]

It shukd be int do I thought it woukd infer that

[FRQDO]

Documentation says it's String? -- which would explain why "3" + "5" == "35"

You can, for example, try using ?.toInt() on the inputs

[Daniel Pitts]

It looks like it is adding, but the expected output is multiplying.

[Daniel Pitts]

Oh, never mind, Richard is correct, and I'm just misreading it.

[FRQDO]

While Kotlin is great at inferring types, it needs enough information to do that.
The operator fun plus is defined both for `Int`s and for `String`s, so there is no reason in your original code for Kotlin to think you're not talking about `String`s

[Sebastian]

Thanks !!

[Sebastian]

I swear I have does it this way before bu
T I guess not

[Klitos Kyriacou]

readLine() returns a String?.
readLine()?.toInt() returns an Int?.
There is no + operator between nullable Int? types; you'd have to use readLine()!!.toInt() or the shorter, more readable form: readln().toInt().

[Daniel Pitts]

or the more appropriate readLine()?.toIntOrNull() ?: error("unable to read integer") Edit: Never mind, I'm sleepy.

[FRQDO]

Good catch, @Klitos Kyriacou!

[Klitos Kyriacou]

> or the more appropriate readLine()?.toIntOrNull() ?: error("unable to read integer")
Why? Just readln().toInt() alone gives you much more appropriate error messages than the cryptic IllegalStateException that error produces.

[Daniel Pitts]

Fair enough.

[Daniel Pitts]

I'm not fully awake 😉

[Sebastian]

Lemme play with this once my boss ain't looking haja

[Sebastian]

It only worked will non nullable. The only safe ? Still failed

[Sebastian]

This is the error when I try the only safe

[Klitos Kyriacou]

This is exactly what I was talking about in my first message. TL;DR: don't use readLine()?.toInt(), use readln().toInt().

[FRQDO]

Yes, that is what Klitos said earlier:

readLine() doesn't give you a String, but a String? -- meaning that it could be a String or null.

The null-safe accessor ?. then says "If the left-hand side is not null, access the right-hand side (toInt() in this case) and use its result; otherwise, just keep using null for whatever code comes next."

String.toInt() would give you an Int, but because of the ?. instead of just ., a null-value String would mean "[...] just keep using null for whatever code comes next" in the above description.
Thus, you end up with the type Int? -- something that could be an Int or null.

The default implementation knows how to add two Int values together, but is not defined for adding a number to the Endless Void, so the compiler will only let you use it when the value is guaranteed to not be null.

This is what various of the aforementioned code snippets do: Prevent your first var from being able to become null, and thus forcing its type to be Int rather than Int?.

[FRQDO]

Aaaand Klitos was slightly faster than I was 🙃

[Klitos Kyriacou]

But that's a good, much fuller, explanation.

[Sebastian]

Your guys are awesome, thank you

[Sebastian]

I didn't realize readLine() was so old lol