Checking the value of an Optional Bool
When I want to check if an Optional Bool is true, doing this doesn't work:
var boolean : Bool? = false
if boolean{
}
It results in this error:
Optional type '@IvalueBool?' cannot be used as a boolean; test for '!= nil' instead
I don't want to check for nil; I want to check if the value returned is true.
Do I always have to do if boolean == true if I'm working with an Optional Bool?
Since Optionals don't conform to BooleanType anymore, shouldn't the compiler know that I want to check the value of the Bool?
Answer
With optional booleans it's needed to make the check explicit:
if boolean == true {
...
}
Otherwise you can unwrap the optional:
if boolean! {
...
}
But that generates a runtime exception if boolean is nil - to prevent that:
if boolean != nil && boolean! {
...
}
Before beta 5 it was possible, but it has been changed as reported in the release notes:
Optionals no longer implicitly evaluate to true when they have a value and false when they do not, to avoid confusion when working with optional Bool values. Instead, make an explicit check against nil with the == or != operators to find out if an optional contains a value.
Addendum: as suggested by @MartinR, a more compact variation to the 3rd option is using the coalescing operator:
if boolean ?? false {
// this code runs only if boolean == true
}
which means: if boolean is not nil, the expression evaluates to the boolean value (i.e. using the unwrapped boolean value), otherwise the expression evaluates to false