Allocations in Rust series

blog/2019-02-09-summary/index.mdx

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+---
+slug: 2019/02/summary
+title: "Allocations in Rust: Summary"
+date: 2019-02-09 12:00:00
+authors: [bspeice]
+tags: []
+---
+
+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:
+
+<!-- truncate -->
+
+**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.
+
+**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.
+
+
+**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.
+
+![Container Sizes in Rust](./container-size.svg)
+
+-- [Raph Levien](https://docs.google.com/presentation/d/1q-c7UAyrUlM-eZyTo1pd8SZ0qwA_wYxmPZVOQkoDmH4/edit?usp=sharing)