1.5 KiB
Optional Values
A very common use case is values that may or may not be present. You could represent this case using enums like so:
enum MaybeInt(AnInt(x:Int), NoInt)
func maybe_takes_int(maybe_x:MaybeInt):
when maybe_x is AnInt(x):
say("Got an int: $x")
else:
say("Got nothing")
However, it's overly onerous to have to define a separate type for each situation where you might want to not have a value. Instead, Tomo has built-in support for optional types:
func maybe_takes_int(x:Int?):
if x:
say("Got an int: $x")
else:
say("Got nothing")
This establishes a common language for talking about optional values without
having to use a more generalized form of enum which may have different naming
conventions and which would generate a lot of unnecessary code.
In addition to using conditionals to check for null values, you can also use
or to get a non-null value by either providing an alternative non-null value
or by providing an early out statement like return/skip/stop or a function
with an Abort type like fail() or exit():
maybe_x := 5?
>> maybe_x or -1
= 5 : Int
>> maybe_x or fail("No value!")
= 5 : Int
maybe_x = !Int
>> maybe_x or -1
= -1 : Int
>> maybe_x or fail("No value!")
# Failure!
func do_stuff(matches:[Text]):
pass
for line in lines:
matches := line:matches($/{..},{..}/) or skip
# The `or skip` above means that if we're here, `matches` is non-null:
do_stuff(matches)