Redundant phrasing

[seishun]

• I have searched open and closed issues and pull requests for duplicates, using these search terms:
  • an instance of a Button or a SelectBox
• I have checked the latest main branch to see if this has already been fixed, in this file:
  • src/ch17-02-trait-objects.md

URL to the section(s) of the book with this problem: https://rust-book.cs.brown.edu/ch17-02-trait-objects.html#using-the-trait

Description of the problem:

It doesn’t check whether a component is an instance of a Button or a SelectBox, it just calls the draw method on the component.

"a Button" already means an instance, so "an instance" is redundant.

Suggested fix:

"an instance of Button or SelectBox" or "a Button or a SelectBox".

[willcrichton]

I would keep the wording as-is just because the rest of the passage uses "instance" to differentiate between a type and a value of that type. I agree it's a little redundant, but it's reasonable to be maximally clear to avoid confusion in these abstract discussions.

[seishun]

One of the fixes I suggested keeps the "instance".