There's a cost to __not__ adding instances as well, namely that accidental need of the class functions (e.g. after abstraction) doesn't fit the library.

Since there's a cost, we need to make sure there's a larger benefit before we decide not to add them -- e.g. a hypothetical or real risk.

2016-03-09 18:12 GMT-08:00 <amindfv@gmail.com>:

My point is that there's a cost to adding instances -- namely that accidental calling of the class functions (e.g. after refactoring) isn't caught by the compiler.

Since there's a cost, we need to make sure there's a larger benefit before we add them -- e.g. a hypothetical or real use-case.

Tom

> El 9 mar 2016, a las 20:28, Fumiaki Kinoshita <fumiexcel@gmail.com> escribió:
>
> Thinking an instance non-practical does not imply we *never* use the instance. The lack of a uniquely legal instance turns out to be a problem at some point, maybe right now.