Allocations in Rust series

blog/2019-02-09-summary/_article.md

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+---
+layout: post
+title: "Summary: What are the Allocation Rules?"
+description: "A synopsis and reference."
+category:
+tags: [rust, understanding-allocations]
+---
+
+While there's a lot of interesting detail captured in this series, it's often helpful to have a
+document that answers some "yes/no" questions. You may not care about what an `Iterator` looks like
+in assembly, you just need to know whether it allocates an object on the heap or not. And while Rust
+will prioritize the fastest behavior it can, here are the rules for each memory type:
+
+**Heap Allocation**:
+
+- Smart pointers (`Box`, `Rc`, `Mutex`, etc.) allocate their contents in heap memory.
+- Collections (`HashMap`, `Vec`, `String`, etc.) allocate their contents in heap memory.
+- Some smart pointers in the standard library have counterparts in other crates that don't need heap
+  memory. If possible, use those.
+
+**Stack Allocation**:
+
+- Everything not using a smart pointer will be allocated on the stack.
+- Structs, enums, iterators, arrays, and closures are all stack allocated.
+- Cell types (`RefCell`) behave like smart pointers, but are stack-allocated.
+- Inlining (`#[inline]`) will not affect allocation behavior for better or worse.
+- Types that are marked `Copy` are guaranteed to have their contents stack-allocated.
+
+**Global Allocation**:
+
+- `const` is a fixed value; the compiler is allowed to copy it wherever useful.
+- `static` is a fixed reference; the compiler will guarantee it is unique.
+
+![Container Sizes in Rust](/assets/images/2019-02-04-container-size.svg) --
+[Raph Levien](https://docs.google.com/presentation/d/1q-c7UAyrUlM-eZyTo1pd8SZ0qwA_wYxmPZVOQkoDmH4/edit?usp=sharing)