GoKawiilDeep dive explains how Rust's dyn Trait represents vtables in memory
A developer blog post dissects how Rust implements runtime polymorphism through dyn Trait, comparing it to C++'s virtual functions and CRTP patterns. The author walks through experiments and diagrams showing exactly how vtable pointers and fat pointers are laid out in memory when using trait objects, with all code published on GitHub.
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Understanding memory layout for dynamic dispatch is crucial for systems programmers optimizing performance-sensitive Rust code, especially those coming from C++ backgrounds who need to unlearn direct 1:1 comparisons between the two languages' polymorphism models. This kind of low-level explainer helps developers build accurate mental models rather than relying on misleading analogies.
- Rust's dyn Trait uses fat pointers containing both data and vtable pointers, unlike C++'s embedded vtable pointer approach
- The post cautions against treating Rust as 'C++ with different syntax' when learning its polymorphism model
- All example code and memory experiments are shared publicly on GitHub for readers to explore
Rust Atomics and Locks by Mara Bos — The article's author credits Mara Bos' book as a core learning resource, and this is it — a deep dive into Rust concurrency, memory ordering and low-level internals. If you enjoy dissecting what Rust actually does in memory, it's a natural next read after poking at vtables.
See Rust Atomics and Locks by Mara Bos on Amazon → Affiliate link — we may earn a commission on purchases, at no extra cost to you. Product picked by AI based on this article; it is not a tested recommendation.Source: sofiabelen.github.io, 2026-09-05
Published there as: “Visualizing Rust's Vtables: How dyn Trait Works In Memory”
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