On Fri, Jan 9, 2015 at 11:40 AM, Keean Schupke <[email protected]> wrote:
> The problem us not with specialisation, its with two or more instances for > the same type. > > As long as one instance is more specific I don't have a problem with them > overlapping, I don't know if anyone else had an issue? > Actually, yes. There is a sleeping bear here that we need to be careful not to poke. Suppose you initially have two overlapping instances for something. One is very specific, while the other is the general case. My program compiles happily against these two instances. Later, you update your library, adding a second specific instance. As it happens, this is the one that I would now choose if I were compiling against your library. The sleeping bear is this: any change to a library that changes how instance resolution proceeds in the importer is necessarily a change in the library version, lest we inadvertently introduce incoherency through this sort of change. shap
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