In context of typespecs:

mfa()	{module(), atom(), arity()}

For child_spec() Erlang uses mfargs() to refer to a {M,F,A} tuple (module, function atom, arguments list - Kernel.apply/3, :erlang.apply/3).

Its a good question! The nearest I could find was an erlang type definition in the docs at Types and Function Specifications — Erlang System Documentation v29.0.2

This has recently come up for me as I am working on a library where I am adding support for a “function reference” argument. Previously I was expecting {module, function, args} even though the args component was not really used for anything simply because that format seems to be universal in Elixir. But due to a behavior change I really need to know what arity to expect and I’m sort of at a loss when it comes to best practice!

I am using NimbleOptions and there is no built in support for this. In fact, the documentation has this line which was puzzling to me right off the bat:

:mfa - A named function in the format {module, function, arity} where arity is a list of arguments. For example, {MyModule, :my_fun, [arg1, arg2]}.

(There is also {:fun, arity} but in my use case the module is also variable, edit: and also on closer reading this appears to be for functions of set arity?)

I have to wonder why it seems that in Elixir mfa has come to mean specifically the args variation and I don’t think I’ve seen a mfargs type in the wild…