[perlgeek]

On a tangent, how long-lived are feature toggles usually?

I have very limited experience, and it points to a wide range from a few days to few months. When I stumble about a 1y+ old flag, I tend to delete it (and the dead code path that it comes with).

What's your experience?

[kevan]

Our feature toggles have tended to live for months to years. Sometimes the really old ones were our fault for not removing, for example we rewrote our payments UI in mid-2014 and the flag stayed around for more than a year after we were at 100%.

Other times integration with third-party tools was what held us back. We rewrote our product pages in 2013 but our recommendations vendor was scraping the old version until 2015 because no one wanted to spend the vendor hours switching it to the new version.

My favorite was our add-to-cart actions. In the old platform we ended up with about 10 different user flows after clicking the "Add to cart" button from 2013-2016. This case was driven by heavy AB testing (should we show a confirmation modal? tooltip? send them to the cart page? what about an interstitial page that shows recommended add-on products? etc). In this case we accepted the overhead of lots of feature switches because a .1% conversion bump moved the needle pretty far.

The shorter flags have lived for a couple months as we build a new feature and then test into it at small percentages to work the bugs out. Once they're in at 100% and we're confident we rip the flag out.

[pkaeding]

In my experience, there are a few different types of feature toggles. Some are permanent, and are useful for operational tasks, like putting an application into read-only mode, or disabling one service that is overloaded to prevent a cascading failure.

For the temporary type of toggle, which is what I was addressing with this blog post, my experience coincides with yours-- usually a few weeks.

The trick with deleting a year-old flag (which I was trying to address with this post) was that you need to be careful when deleting code that you haven't worked on in over a year. If you have the list of necessary changes all pre-baked in a branch, this can be at least a little easier.

[kazinator]

Feature toggles can last decades.

For instance GCC has a feature flag called -ansi which gives you C90 compatibility.

C90 was superseded in 1999 by C99, and so that's 17 years of compatibility, and counting.

[startling]

I don't think this is a feature flag in the same way the rest of the discussion is using the phrase.

[kazinator]

How so? C99+ support/conformance is a compiler feature. That feature breaks/conflicts with some aspects of C90 support, an existing, older feature. So you need a feature flag. Inside comiler there are various places where you have the equivalent of "if C90 do this, else do that".

[startling]

"Feature flags" tend to be for behavior that is being developed and tested. The -ansi flag is more like configuration. It's pretty valuable to continue to support C90.