Draft: generics section of structs chapter

[steveklabnik]

A light introduction to syntax.

[steveklabnik]

r? @aturon

[sophiajt]

I like starting out with concrete and then taking it generic.

For this example, I was wondering if it should start even simpler. Eg) just struct Point { ... } without any derives. Helps us to minimize concept count a bit and also helps avoid them later passing a type that doesn't satisfy one of these traits and getting a confusing error.

[steveklabnik]

We dealt with the derives and such in the previous section.

[sophiajt]

@steveklabnik - I suspect people will likely not read from front to back, and that they'll often come here from googling "generics in Rust" or something similar. If possible, it may help to limit the concept count in any given section/chapter to what's necessary for that chapter to help readability for those types of readers (at the very least, limit concept count for your motivating example...)

[steveklabnik]

The book is really meant to read front to back, unfortunately, or at least, it's not intended to be reference-style, but "read this in order to learn Rust."

[steveklabnik]

Okay everyone, I have pushed a few things to address most of the comments here. I'm going to merge this one now, please open issues if there's anything else particularly important.