Callbacks

You can of course use callbacks in Vapour but you can make them more robust by setting custom types for callbacks so that functions that accept callbacks will check for the signature of callbacks passed to them.

note

This is the only place in Vapour where types are not preceded by a colon :

We can thus define a type for a function signature below: it expects an int as argument and must return an int

type math: func(int, int) int

With the type define we can reference that type in other functions where we want to use a function of that signature as callback. This ensures that we only pass functions that corresponds to our predefined expectations.

func vectorise_math(x: int, y: int, cb: math): int {
  return cb(x, y)
}

We can then use the function defined above

vectorise_math(1, 2, (x: int, y: int): int => {
  return x * y
})

vectorise_math(1, 2, (x: int, y: int): int => {
  return x + y
})

This ensures that we catch instances where we pass functions that do not have the right signature, as shown below where the callback returns a num instead of an int.

# will fail, callback is of the wrong signature.
vectorise_math(1, 2, (x: int): num => {
  return x / 2
})