Cheatsheet recap

One line per idea, in order. The pause-for-questions slide.

Idea	Remember
Three collections	same rules. new shapes.
Why a Vec?	list. heap. owned.
Making a Vec	macro for known values. `new` for empty. capacity for big.
Changing a Vec	push, pop, insert. always an Option on pop.
Reading a Vec	`.get` for safe. `&` to iterate. len isn't capacity.
&str vs String	literal: `&str`. runtime text: `String`. accept `&str`.
Strings are UTF-8 bytes	english fits one byte. one cat does not.
Why s[0] doesn't compile	ask for chars or bytes. never `s[0]`.
Building strings	`+` moves the left. `format!` borrows.
Why a HashMap?	lookup by name. owned, like the rest.
Using a HashMap	get returns an Option. order is arbitrary.
Who owns the keys?	String moves. u32 copies. a `&` must outlive the map.
The check-then-insert mess	two lookups. there's a better way.
The entry API	one lookup. then decide.
Borrow while iterating	same borrow rule. new shape.
Read all, then write all	read all. then write all.

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