Design pattern: User-defined functor in Motoko

[matthewhammer]

This issue is tracking the answer to the question: How does one write what could be an SML/OCaml-style functor in Motoko, using the current language features?

As one example (WIP): Adapton functor from the Adapton package.

[matthewhammer]

The HashMap class from base is doing an instance of this pattern (it accepts types and associated functions in its constructor), but not as a single module/record argument. Still, it serves as another example.

[rossberg]

Isn't this issue more appropriate for the main Motoko repo? Any decent answer would involve changes to the language.

[matthewhammer]

Isn't this issue more appropriate for the main Motoko repo? Any decent answer would involve changes to the language.

Okay, but if we move this discussion, should we also move the other one (about "a style guide")?

(Is this not just another question about style? "Birds of a feather"...?)

[matthewhammer]

Summarizing @rossberg from the team meeting:

• If there's no state, can/should use a function over the class, returning a module (not an object).

(But here I am using state in the returned object, so perhaps a class is best after all?)

• The class's types would be simpler to define if we could define types with free type vars. That's a language/compiler restriction that may be lifted in the near future.

I think the answer posed by the issue has been sufficiently answered for me, for now.