There are several members here who are very quick to remind posters that an addon is All Rights Reserved. Generally, the reminder comes after someone mentions an intention to look into how something is done in an addon and implies or states that they want to use that information, but are not specific enough in their description of their plans as to make it clear whether their actions would infringe upon the other author's copyright.
I understand that exchange, I think. But, when I've tried to, as a mental exercise, re-imagine those scenarios such that I'm making the post but such that I've added enough extra information to make it clear that I'm in the right ... I've never reached a satisfactory conclusion.
For example: (Say) I've found a need to implement a UnitID:GUID map, and so I make a survey of the addons I have installed to find ones that maintain such a map and to see the details of how it is implemented and used in the addon code at large.
As I see it, there are a (practically) finite number of ways to implement and use a UnitID:GUID map under the WoW API and in Lua. What part of an implementation of a UnitID:GUID map would fall under the author's copyright? A facile answer might be: "any novel portion of the implementation". Well, what qualifies as "novel" changes as one's skill in a language improves. Moreover, if we accept the "novel" criteria and move forward: if I were to learn something I didn't know about addon development while looking through an addon's code and that technique or method was considered part of what made that code "novel", then what can I realistically do, at that point? I can't erase what I learned -- it will come to me when I try to solve any similar problem in the future, just like all the other tools in my programming toolbox.
Perhaps some of you can help me wrap my brain around this. It is my opinion that responding to posts with, "You can't copy any of that code. That addon is All Rights Reserved," is not constructive if it's not readily apparent what that actually means.