Using Combine update - reference content complete!

I'm thrilled to be announcing that an updated version of Using Combine is now available! 

It has taken me nearly 6 months to draft it all, reverse engineering and writing tests for all the various publishers, operators, and pieces in between - and documenting what I found. The end result is 182 pages (in US PDF format) of reference documentation the way I would generally like to have it.

While the live site ( is updated automatically, updated PDF and ePub versions are now available on Gumroad ( If you purchased a copy previously, you can go to Gumroad and get updated, DRM free, content in either PDF or ePub formats.

This updates finishes the largest swath of reference updates, creating tests to verify all the various operators and writing the documentation reference sections for the following:

- mapping operators

- filtering operators

- sequence operators

- math operators

- criteria operators

- reducing operators

I even managed to slip in a marble diagram or two, although not every operator or publisher has the diagramming.

There was also an update for Xcode 11.3 and associated iOS 13.3 and macOS 10.15.2, which included some subtle changes to the throttle operator behavior. The tests that I wrote early on came in extraordinarily helpful, and I wrote in more detail about it on my personal blog (

With this update, the majority of the core content is now complete, but the work is by no means finished.

The next steps for the book are review and editing. On the list includes refining the descriptions of the reference sections, reviewing all the patterns now that we have had Combine for a few months, and seeing the updates as the API changes and refines. In just glancing through the finished PDF and ePub I spotted a number of errors and flaws that I'm collecting for the next big editing pass. There are some marble diagrams now, but more are likely needed in some sections - both in the patterns and reference sections.

As before, this continues as a labor of love and for the community. Meaning that the content will continue to be free, available on the live site (, with updates being made available as I make them. The work has been financially supported by 116 people as I'm writing this, as well as a number of people providing pull requests to fix typos and grammar flaws. It has by no means been a solo project, so thank you for helping me get this out there and maintain it.