[Rd] vctrs: a type system for the tidyverse

[Hadley Wickham]

> > As Gabe mentioned (and you've explained about) the term "type"
> > is really confusing here.  As you know, the R internals are all
> > about SEXPs, TYPEOF(), etc, and that's what the R level
> > typeof(.) also returns.  As you want to use something slightly
> > different, it should be different naming, ideally something not
> > existing yet in the R / S world, maybe 'kind' ?
>
> Agreed - I've been using type in the sense of "type system"
> (particularly as it related to algebraic data types), but that's not
> obvious from the current presentation, and as you note, is confusing
> with existing notions of type in R. I like your suggestion of kind,
> but I think it might be possible to just talk about classes, and
> instead emphasise that while the components of the system are classes
> (and indeed it's implemented using S3), the coercion/casting
> relationship do not strictly follow the subclass/superclass
> relationships.

I've taken another pass through (the first part of) the readme
(https://github.com/r-lib/vctrs#vctrs), and I'm now confident that I
can avoid using "type" by itself, and instead always use it in a
compound phrase (like type system) to avoid confusion. That leaves the
`.type` argument to many vctrs functions. I'm considering change it to
.prototype, because what you actually give it is a zero-length vector
of the class you want, i.e. a prototype of the desired output. What do
you think of prototype as a name?

Do you have any thoughts on good names for distinction vectors without
a class (i.e. logical, integer, double, ...) from vectors with a class
(e.g. factors, dates, etc). I've been thinking bare vector and S3
vector (leaving room to later think about S4 vectors). Do those sound
reasonable to you?

Hadley

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