For example take the JSON decoder. If you have several tasks which can use some data from a JSON blob in parallel, is it OK if they all just share the same JSON decoder?
If you're horrified because this seems obviously like a bad idea, that'll be why you didn't find any trouble. In some other systems your programs would be needlessly slow and clunky as a result, but in Go your assumptions were appropriate.
It seems Groxx expects in this case that either the JSON decoder would work fine used this way, or, the documentation would highlight that you can't do this. Go chooses neither.
Here's Brad Fitzpatrick:
"The assumption when unstated is that things are not safe for concurrent use, that zero values are not usable, that implementations implement interfaces faithfully, and that only one return values is non-zero and meaningful."
These are some pretty important assumptions, or to look at it another way, potential foot guns.
