Comparing Optionals

We now know how to access the value of an optional variable, but how do we check if the variable actually holds a valid value at all? It's pretty simple, actually. Any optional value can bo compared with the none literal, so we can compare for equality / inequality extremely easily. Here is an example of that:

use Core.print

def main():
    i32? maybe = none;
    if maybe == none:
        print("has no value\n");

    maybe = 69;
    if maybe != none:
        print($"has value: {maybe!}\n");

This program prints these lines to the console:

has no value
has value: 69

But why can we compare any optional variable with none (including none itself)? Here is a small fun fact on how this is within the compiler: The none literal actually has the type void?, so its either nothing or nothing, so it's really nothing after all!

But we cannot only compare optional values to the none literal, but to other optional values too:

use Core.print

def main():
    i32? maybe_1 = none;
    i32? maybe_2 = none;
    if maybe_1 == maybe_2:
        print("are equal\n");

    maybe_1 = 69;
    if maybe_1 != maybe_2:
        print($"are inequal, maybe_1 = {maybe_1!}, maybe_2 = 'none'\n");

    maybe_2 = 420;
    if maybe_1 != maybe_2:
        print($"are inequal, maybe_1 = {maybe_1!}, maybe_2 = {maybe_2!}\n");

    maybe_2 = 69;
    if maybe_1 == maybe_2:
        print($"are equal, maybe_1 = {maybe_1!}, maybe_2 = {maybe_2!}\n");

This program will print these lines to the console:

are equal
are inequal, maybe_1 = 69, maybe_2 = 'none'
are inequal, maybe_1 = 69, maybe_2 = 420
are equal, maybe_1 = 69, maybe_2 = 69

So, you can see that two variables of type i32? match if either they are both none or their actual values match. If one of them is none but the other one is not, they do not match, and same goes when both have a value but that value differs, then they also do not match. As you can see, we have used quite a bit of unwrapping (!) in this example and the program would definitely crash if we would set both variables to none before the last if statement. So, you still need to use the unwrapping with caution.