unexpected behaviour of R.once if the wrapped function throws an error.

[adrian-gierakowski]

Currently, if during first call the wrapped function throws an error and the error is handled, each subsequent call will return undefined.

This is due to the fact that called is set to true before the function is called:

ramda/source/once.js

Lines 31 to 32 in ed191e6

	called = true;
	result = fn.apply(this, arguments);

Consider this example:

const Promise = require('aigle')

const wrappedFunc = () => {
  // Some code which due to a bug throws an error
}

const onceWrappedFunc = R.once(wrappedFunc)

P.retry({ times: 4 }, () => onceWrappedFunc())
  .then(result => console.log('result', result))
  .catch(error => console.log('error', error))

We are going to end up with .then callback being called with undefined instead catch callback being called with an error.

I think the most reasonable behaviour would be for R.once to store the error which happens during the first call and re-throw it on each subsequent call.

An alternative would be to swap the two lines of code quoted at the top of this message, but that would cause the wrappedFunc to be called multiple times, which breaks the expectation that it should only be ever called once.

[Bradcomp]

I definitely think it's right for called to be set regardless of whether the function succeeds.

I can see the benefit for capturing and rethrowing the error each time. Would you be interested in opening a PR?

[adrian-gierakowski]

@Bradcomp sure, I’ll submit a PR tomorrow.

[CrossEye]

@adrian-gierakowski: Are you still interested in creating a PR?

[adrian-gierakowski]

Yes, I’ve got an implementation ready.

[CrossEye]

Great! Feel free to post a PR with it. We're trying to clean up all sorts of old issues on the way to getting v1.0 out the door.

[adrian-gierakowski]

Oh, v1 finally. Nice!

[CrossEye]

We're trying... finally!