vrod
I am working with behaviours and callbacks, so I am trying to define a spec for a function that should accept an argument which is also a function, but specifically a function that accepts 1 argument. I just discovered that there is a is_function that can be used in a guard clause: Kernel — Elixir v1.20.2
I have something like this:
@callback something(fun :: function()) :: list()
and implementations look like this:
@impl true
def something(fun) do
fun.("abc")
end
It is important that the provided fun has an arity of 1. I could make a guard clause:
@impl true
def something(fun) when is_function(fun, 1) do
fun.("abc")
end
but I am wondering if it is possible to define this in the @callback spec?
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Marcus
You can try:
hauleth
Of course
(term() -> term()), but it will not enforce it in any way.dimitarvp
Yes, you can make a typespec for a function as well and then put it in the
@callbackdefinition. Or it can be put inline as @Marcus demonstrated.eksperimental
You can read the Typespecs page, specifically the tables in Typespecs reference — Elixir v1.20.2 when in doubt.
vrod
Ah, I did not realize that this is how you can annotate anonymous or captured functions:
However, why won’t this be enforced as the other types are enforced?
hauleth
It will be checked in most cases, not enforced. Nothing will prevent you from doing invalid call to such function.
eksperimental
As of now, the only type check that happens at compile time is determined by guards and pattern matching in function definitions (if I understand correctly how these new checks happen), not based on typespecs.
ityonemo
generally typespecs are not enforced in the BEAM at all. The function/arity typespecs are kind of deficient and (IMO) incorrect as implemented in dialyzer currently, I made an opinion video about here: https://www.youtube.com/watch?v=_XSRsYSwNpQ
rvirding
Well elixir is dynamically typed so the checks aren’t done at compile time as such but the compiler adds code which do the checks in the patterns and guards. The compiler quite happily ignores all your type specs though you can use the dialyzer tool which will try to check your code and warn you if it finds errors.