Create some type aliases for string Contexts

[Ericson2314]

No description provided.

[thufschmitt]

Just a small nit, but do what you want with it ;)

[thufschmitt]

Maybe remove this and use NixStringContext::value_type instead? Doesn’t change much, but I find it more explicit

[Ericson2314]

Or maybe it should be this way to be consistent with SearchPathElem. which I had completely forgotten about in the time since I first wrote this code.

[edolstra]

Not sure this is really an improvement. If I see std::pair<std::string, std::string> I know what it means, but if I see NixStringContextElem I have to look up what that type means. I.e. more cognitive overhead.

[Ericson2314]

@edolstra The problem with std::pair<std::string, std::string> is that there are many other uses which don't have to do with the string context. Without having the alias (or better yet, writing a struct) one doesn't know which ones are for which purpose.

Concretely this also made #6237 easy (baring the GCC bug) because I could just change the definition in one spot.

[Ericson2314]

Also c.f. SearchPathElem in this file, added by you in 363f37d ! :)

[fricklerhandwerk]

@edolstra Naming types by what they mean is always better for readability. There are so many arguments for creating (the right!) abstractions, and the idea is so commonplace, that any serious source I can think about citing would already sound corny and stereotyped.

[Ericson2314]

#6237 This contains and motivates this, so I will close this in lieu of that.