More sketching

_drafts/a-heaping-helping.md

@@ -72,11 +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
-- Boxed closures (FnBox, others?) are heap allocated
-- "Move" semantics don't trigger new allocation; just a change of ownership,
-  so are incredibly fast
-  - In examples, is address of data before and after the same?
-  - Can `Copy` trigger allocation?
+- `lazy_static!` and `thread_local!` force heap allocation
 - Stack-based alternatives to standard library types should be preferred (spin, parking_lot)
 
 # Smart pointers
@@ -96,8 +92,8 @@ crate should look mostly familiar:
 - [`Arc`](https://doc.rust-lang.org/alloc/sync/struct.Arc.html)
 - [`Cow`](https://doc.rust-lang.org/alloc/borrow/enum.Cow.html)
 
-The [standard library](https://doc.rust-lang.org/std/) also defines some smart pointers,
-though more than can be covered in this article. Some examples:
+The [standard library](https://doc.rust-lang.org/std/) also defines some smart pointers
+to manage heap objects, though more than can be covered here. Some examples:
 - [`RwLock`](https://doc.rust-lang.org/std/sync/struct.RwLock.html)
 - [`Mutex`](https://doc.rust-lang.org/std/sync/struct.Mutex.html)
 
@@ -168,4 +164,29 @@ But because the vector has no elements it is managing, no calls to the allocator
 will ever be dispatched. A couple of places to look at for confirming this behavior:
 [`Vec::new()`](https://doc.rust-lang.org/std/vec/struct.Vec.html#method.new),
 [`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).
+and [`String::new()`](https://doc.rust-lang.org/std/string/struct.String.html#method.new).
+
+# **thread_local!** and **lazy_static!**
+
+# Heap Alternatives
+
+While it is a bit strange for us to talk of the stack after spending so much time with the heap,
+it's worth pointing out that some heap-allocated objects in Rust have stack-based counterparts
+provided by other crates. There are a number of cases where this may be helpful, so it's useful
+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
+[parking_lot](https://crates.io/crates/parking_lot). 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)
+if you're in need of synchronization primitives.
+
+[thread_id](https://crates.io/crates/thread-id)
+may still be necessary if you're implementing an allocator (*cough cough* the author *cough cough*)
+because [`thread::current().id()`](https://doc.rust-lang.org/std/thread/struct.ThreadId.html)
+[uses a `thread_local!` structure](https://doc.rust-lang.org/stable/src/std/sys_common/thread_info.rs.html#22-40)
+that needs heap allocation.

_drafts/compiler-optimizations.md

@@ -34,6 +34,44 @@ There will, however, be an opera of optimization.
 
 # The Case of the Disappearing Box
 
+```rust
+// Currently doesn't work, not sure why.
+use std::alloc::{GlobalAlloc, Layout, System};
+use std::sync::atomic::{AtomicBool, Ordering};
+
+fn allocate_box() {
+    let x = Box::new(0);
+}
+
+pub fn main() {
+    // Turn on panicking if we allocate on the heap
+    DO_PANIC.store(true, Ordering::SeqCst);
+    
+    allocate_box();
+}
+
+#[global_allocator]
+static A: PanicAllocator = PanicAllocator;
+static DO_PANIC: AtomicBool = AtomicBool::new(false);
+struct PanicAllocator;
+
+unsafe impl GlobalAlloc for PanicAllocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        if DO_PANIC.load(Ordering::SeqCst) {
+            panic!("Unexpected allocation.");
+        }
+        System.alloc(layout)
+    }
+    
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        if DO_PANIC.load(Ordering::SeqCst) {
+            panic!("Unexpected deallocation.");
+        }
+        System.dealloc(ptr, layout);
+    }
+}
+```
+
 # Vectors of Usual Size
 
 # Dr. Array or: How I Learned to Love the Optimizer

_drafts/stacking-up.md

@@ -98,6 +98,8 @@ With all that in mind, let's talk about situations in which we're guaranteed to
 - [Arrays](https://doc.rust-lang.org/std/primitive.array.html) are always stack-allocated.
 - Closures capture their arguments on the stack
 - 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.
 
 # Structs
 
@@ -445,4 +447,28 @@ pub fn do_call() {
 -- [Compiler Explorer](https://godbolt.org/z/u_yguS)
 
 It's hard to imagine practical situations where dynamic dispatch would be
-used for objects that aren't heap allocated, but it technically can be done.
+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
+[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:
+[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`
+(move semantics for stack objects vs. copying stack pointers vs. copying stack `struct`s), 
+*it's impossible for `Copy` to introduce a heap allocation*.
+
+But why is this the case? Fundamentally, it's because the language controls
+what `Copy` means -
+["the behavior of `Copy` is not overloadable"](https://doc.rust-lang.org/std/marker/trait.Copy.html#whats-the-difference-between-copy-and-clone)
+because it's a marker trait. From there we'll note that a type
+[can implement `Copy`](https://doc.rust-lang.org/std/marker/trait.Copy.html#when-can-my-type-be-copy)
+if (and only if) its components implement `Copy`, and that
+[no heap-allocated types implement `Copy`](https://doc.rust-lang.org/std/marker/trait.Copy.html#implementors).
+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?