[pdpi]

It’s a riff on Heisenberg’s uncertainty principle — a bug that changes behaviour when you try to observe it, typically the sort of bug that you can’t reproduce under debug conditions. Often they’re race conditions or other timing-sensitive bugs, and the debugger changes timings enough that the bug doesn’t trigger.

[Consultant32452]

I fondly remember a bug that only appeared when print statements were removed. The i/o of the system out was just long enough for some buffer to clear, making the app work. That was very annoying.

[aloer]

earlier today I had a problem with Xcode always opening the wrong file, a README

Turns out I am not the only one: https://stackoverflow.com/questions/53132398/xcode-10-1-open...

half a year old at least, as long as the first file is a readme it will open that one instead of the actually clicked file in a new window no matter what. Only fix is to remove the file

but if Xcode is instead set to open as new tab instead of new window, instead everything works just fine.

[meddlepal]

This is a very common one with concurrent code. I've seen many cases where something works most of the time until a log statement is removed.

[ThrowawayR2]

> It’s a riff on Heisenberg’s uncertainty principle — a bug that changes behaviour when you try to observe it...

As an aside, the Heisenbug is erroneously named because the phenomenon being described is actually the observer effect ( https://en.wikipedia.org/wiki/Observer_effect_(physics) ). The uncertainty principle refers to something entirely different.