Getting “use of undeclared type 'NoError'”

问题:

I am trying to learn ReactiveCocoa and have a hard time getting started. I keep hitting minor bumps as API and tutorials seems to be outdated quickly. Maybe I have the wrong impression.

Just trying to follow this I do not seem to have NoError.

It should be imported correctly, since I have access to Signal, rac_textSignal etc. but I don't know why NoError is not available.

Their documentation mentions NoError as well but that leads to a 404.

This transition to RAC4 mentions NoError as well. Why is NoError undeclared? I am using ReactiveCocoa 4.0.1.

Edit: I just added public enum NoError : ErrorType {} to the top of the file and it works now. I am not sure if this is a proper solution to the problem though. It is not mentioned in guides and tutorials that I should extend ErrorType myself.

回答1:

The reactive cocoa native NoError was removed in 4.0.1 in favour of antitypicals implementation in Result (adds NoError to Result, see this). See e.g. issue #2704

• https://github.com/ReactiveCocoa/ReactiveCocoa/issues/2704

We can see this explicitly used in the source files, e.g.

• import enum Result.NoError in Property.swift.

Hence, you probably need to include (antitypicals) Result whenever you intend to use NoError. One suggested fix in the issue thread is

public typealias NoError = Result.NoError

回答2:

If you add "import Results" to the top of the page above your class, NoError will no longer be an undeclared type!