Detecting Generic Type in Motoko

[paulyoung]

A more ergonomic approach might be to have your function accept any type with a toText method as its argument, and then create your own wrapper classes for Nat, Text, and so on that implement that interface.

Something like this:

Idea for CRUD types - feedback appreciated

This is less about your overall design but I just wanted to point out that you can do the following to ensure that the classes are correct when defined rather than deferring that check to one of the call sites. type Type<T> = { get : () -> T; set : T -> (); sanitise : () -> T; validate : () -> Bool; }; class FloatType() : Type<Float> { var value : Float = 0; public func get() : Float { value }; public func set(v : Float) {}; public func sanitise() : Float { value }; public fu…

Or in your case:

type ToText<A> = {
  toText : A -> Text;
};

func toText(x : ToText) : Text {
  return x.toText();
};

This example seems a bit pointless but it can be quite powerful when you implement multiple interfaces in a single type and then deal with abstract values.

I’m not sure if Motoko supports something like func toText<A : ToText, OtherInterface>(x : A) : Text { these days but that would make it more practical.

I was resorting to this hack in the past but it doesn’t help with accepting function arguments that are super types of multiple types or “implement multiple interfaces”:

Idea for CRUD types - feedback appreciated

You can use this hack I came up with to have the type checker verify that a class is a supertype of multiple types. type Flying = { fly : () -> (); }; type Swimming = { swim : () -> (); }; type Walking = { walk : () -> (); }; class Bird() { public func fly() {}; public func walk() {}; }; // Flying <: Bird let _ : () -> Flying = Bird; // Walking <: Bird let _ : () -> Walking = Bird; class Dog() { public func swim() {}; public func walk() {}; }; // Swimming <: Dog let _ : ()…