Interesting analogy. "Ripping" something off an only using it for your personal project sounds like the "playing a movie for a few friends". Doing so for the benefit of corporation that then has thousands of daily visitors sounds like the "movie cinema" example. Though, in both cases it was an individual googling and finding how to implement a specific function.
"fair use" in copyright is pretty specific in that it refers to things like "you can play portions of a clip in order to comment on it." Or as another example, you can use clips/portions for the purposes of a review commentary.
"Form and function" is perhaps a very important crux here. Some things you can only do a certain way. For example, quick-sort, there are is only really one way to implement quick sort (or otherwise it is not at all quick sort!).
Personally I feel the copyright line is higher than a function, the copyright is on the collection of functions who together create a specific software. The individual functions IMHO are as copyright'able as-is a cog on a bike cassette, or the chain on a motorcycle.
