Workaround for async functions with parametric type in Motoko

Overview

Links

The package is published on MOPS and GitHub.

The API documentation can be found here.

For updates, help, questions, feedback and other requests related to this package join us on:

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Motivation

Asynchronous functions, i.e. those whose return type starts with async or async*, cannot have a type parameter in their return type. This package provides a workaround.

Build and test

We need mops installed.

mops test

Example

The following code is desired but not allowed:

module M {
  public func f<T>(x : T) : async* [T] { 
    // some code here
    [x, x] 
  };
};

let f = M.f<Nat>;

await* f(0); // => [0, 0]

Instead, with the generics package, we can do this:

import Generics "mo:generics";

module M {  
  public class f_<T>() {
    let buf : Generics.Buf<[T]> = Generics.Buf<[T]>();
    public func call(x : T) : async* () {
      // some code here
      buf.set([x, x]);
    };
    public func result() : [T] = buf.get();
  };
};

let f_ = M.f_<Nat>();
func f(x : Nat) : async* [Nat] {
  await* f_.call(x);
  f_.result();
};

await* f(0); // => [0, 0]

Install with mops

You need mops installed. In your project directory run:

mops add generics

In the Motoko source file import the package as:

import Generics "mo:generics";

Copyright

MR Research AG, 2024

Authors

Main author: Timo Hanke

License

Apache-2.0