Open-source implementation of Apple's Combine framework for processing values over time.
The main goal of this project is to provide a compatible, reliable and efficient implementation which can be used on Apple's operating systems before macOS 10.15 and iOS 13, as well as Linux and Windows.
The project is in early development.
In order to work on this project you will need Xcode 10.2 and Swift 5.0 or later.
Please refer to the issue #1 for the list of operators that remain unimplemented, as well as the RemainingCombineInterface.swift file. The latter contains the generated interface of Apple's Combine from the latest Xcode 11 version. When the functionality is implemented in OpenCombine, it should be removed from the RemainingCombineInterface.swift file.
You can run compatibility tests against Apple's Combine. In order to do that you will need either macOS 10.14 with iOS 13 simulator installed (since the only way we can get Apple's Combine on macOS 10.14 is using the simulator), or macOS 10.15 (Apple's Combine is bundled with the OS). Execute the following command from the root of the package:
$ make test-compatibility
Or enable the
-DOPENCOMBINE_COMPATIBILITY_TEST compiler flag in Xcode's build settings. Note that on iOS only the latter will work.
NOTE: Before starting to work on some feature, please consult the GitHub project to make sure that nobody's already making progress on the same feature! If not, then please create a draft PR to indicate that you're beginning your work.
Some publishers in OpenCombine (like
Publishers.Merge) exist in several
different flavors in order to support several arities. For example, there are also
Publishers.MapKeyPath3, which are very similar but different enough that Swift's type system
can't help us here (because there's no support for variadic generics). Maintaining multiple instances of
those generic types is tedious and error-prone (they can get out of sync), so we use the GYB tool for
generating those instances from a template.
GYB is a Python script that evaluates Python code written inside a template file, so it's very flexible — templates can be arbitrarily complex. There is a good article about GYB on NSHipster.
GYB is part of the Swift Open Source Project and can be distributed under the same license as Swift itself.
GYB template files have the
.gyb extension. Run
make gyb to generate Swift code from those
templates. The generated files are prefixed with
GENERATED- and are checked into source control. Those
files should never be edited directly. Instead, the
.gyb template should be edited, and after that the files
should be regenerated using