Still need to address lazy_static, thread_local, and iterators

_drafts/a-heaping-helping.md

@@ -72,7 +72,7 @@ we'll follow this guide:
 - Smart pointers hold their contents in the heap
 - Collections are smart pointers for many objects at a time, and reallocate
   when they need to grow
-- `lazy_static!` and `thread_local!` force heap allocation
+- `lazy_static!` and `thread_local!` force heap allocation for everything.
 - Stack-based alternatives to standard library types should be preferred (spin, parking_lot)
 
 # Smart pointers
@@ -166,7 +166,15 @@ will ever be dispatched. A couple of places to look at for confirming this behav
 [`HashMap::new()`](https://doc.rust-lang.org/std/collections/hash_map/struct.HashMap.html#method.new),
 and [`String::new()`](https://doc.rust-lang.org/std/string/struct.String.html#method.new).
 
-# **thread_local!** and **lazy_static!**
+# **lazy_static!** and **thread_local!**
+
+There are two macros worth addressing in a conversation about heap memory. The first isn't part
+of the standard library, but it's the [5th most downloaded crate](https://crates.io/crates/lazy_static)
+in Rust. The second
+
+TODO: Not so sure about lazy_static anymore. Is thread_local possibly heap-allocated too?
+- Think it may actually be that lazy_static has a no_std mode that uses `spin`, std-mode uses std::Once.
+- Reasonably confident thread_local always allocates
 
 # Heap Alternatives
 
@@ -178,8 +186,8 @@ to know that alternatives exist if you need them.
 When it comes to some of the standard library smart pointers
 ([`RwLock`](https://doc.rust-lang.org/std/sync/struct.RwLock.html) and
 [`Mutex`](https://doc.rust-lang.org/std/sync/struct.Mutex.html)), stack-based alternatives
-are provided in crates like [spin](https://crates.io/crates/spin) and
+are provided in crates like [parking_lot](https://crates.io/crates/parking_lot) and
-[parking_lot](https://crates.io/crates/parking_lot). You can check out
+[spin](https://crates.io/crates/spin). You can check out
 [`lock_api::RwLock`](https://docs.rs/lock_api/0.1.5/lock_api/struct.RwLock.html),
 [`lock_api::Mutex`](https://docs.rs/lock_api/0.1.5/lock_api/struct.Mutex.html), and
 [`spin::Once`](https://mvdnes.github.io/rust-docs/spin-rs/spin/struct.Once.html)

_drafts/stacking-up.md

@@ -100,6 +100,10 @@ With all that in mind, let's talk about situations in which we're guaranteed to
 - Generics will use stack allocation, even with dynamic dispatch.
 - [`Copy`](https://doc.rust-lang.org/std/marker/trait.Copy.html) types are guaranteed to be
   stack-allocated, and copying them will be done in stack memory.
+- [`Iterator`s](https://doc.rust-lang.org/std/iter/trait.Iterator.html) in the standard library
+  are stack-allocated. No worrying about some
+  ["managed languages"](https://www.youtube.com/watch?v=bSkpMdDe4g4&feature=youtu.be&t=357)
+  creating garbage.
 
 # Structs
 
@@ -451,12 +455,12 @@ used for objects that aren't heap allocated, but it technically can be done.
 
 # Copy types
 
-Understanding move semantics and copy semantics in Rust is hard. The Rust docs
+Understanding move semantics and copy semantics in Rust is weird at first. The Rust docs
 [go into detail](https://doc.rust-lang.org/stable/core/marker/trait.Copy.html)
 far better than can be addressed here, so I'll leave them to do the job.
-Their guideline is reasonable though:
+Even from a memory perspective though, their guideline is reasonable:
 [if your type can implemement `Copy`, it should](https://doc.rust-lang.org/stable/core/marker/trait.Copy.html#when-should-my-type-be-copy).
-While there are potential speed tradeoffs to benchmark when discussing `Copy`
+While there are potential speed tradeoffs to *benchmark* when discussing `Copy`
 (move semantics for stack objects vs. copying stack pointers vs. copying stack `struct`s), 
 *it's impossible for `Copy` to introduce a heap allocation*.
 
@@ -471,4 +475,19 @@ Thus, assignments involving heap types are always move semantics, and new heap
 allocations won't occur without explicit calls to
 [`clone()`](https://doc.rust-lang.org/std/clone/trait.Clone.html#tymethod.clone).
 
-TODO: Some examples. Maybe just need to show compiler errors?
+```rust
+#[derive(Clone)]
+struct Cloneable {
+    x: Box<u64>
+}
+
+// error[E0204]: the trait `Copy` may not be implemented for this type
+#[derive(Copy, Clone)]
+struct NotCopyable {
+    x: Box<u64>
+}
+```
+-- [Compiler Explorer](https://godbolt.org/z/VToRuK)
+
+# Iterators
+