Hyrum’s Law in Golang

Hyrum's Law is one of those observations that's certainly useful, but be careful not to fixate on it and draw the wrong conclusions. Consider that even the total runtime of a function is an observable property, which means that optimizing a function to make it faster is a breaking change (what if suddenly one of your queues clears too fast and triggers a deadlock??), despite the fact that 99.99999999% of your users would probably appreciate having code that runs faster for no effort on their part.

Therefore it's unavoidable that what constitutes a "breaking change" is a social contract, not a technical contract, because the alternative is that literally nothing is ever allowed to change. So as a library author, document what parts of your API are guaranteed not to change, be reasonable, and have empathy for your users. And as a library consumer, understand that making undocumented interfaces into load-bearing constructs is done at your own risk, and have empathy for the library authors.

I feel like this is approaching absurdity, if only because something like the total runtime of a function is not under the control of the author of the function. The operating environment will have an impact on that, for example, as will the load the system is currently experiencing. A GC pass can affect it.

In short, I wouldn't consider emergent behaviours of a machine as part of an intentional interface or any kind of contract and therefore I wouldn't see it as a breaking change, the same as fixing a subtle bug in a function wouldn't be seen as a breaking change even if someone depended on the unintentional behaviour.

I think it's more of a testament to Go's hardcore commitment to backwards compatibility, in this case, than anything else.

It's quite common in cryptography for the runtime to be important. For example, password verification time shouldn't depend on the value of the key or the password. Systems have been broken because someone wrote a string compare that returned early.