Borrow-checking without type-checking

Jamie Brandon · 22 Apr 2026 · scattered-thoughts.net ↗

2 korrents from this piece

Jamie Brandon did not write this page.

Every claim below was made in this piece, quoted word for word and numbered in the order the piece makes them, so you can read it there rather than take our word for it. The sentence above each quote is our reading of the claim, not their wording. Each quote was checked against a stored copy of the page at build time; where the two differ, the quote is the fact.

Our reading
Layering a static type system atop a dynamic one, capable of proving the dynamic checks redundant, combines the flexibility of dynamic typing with the performance of static typing.

Their wordsThe dynamic type system provides flexibility and easy meta-programming, while the static type system removes the overhead in most of your code.
Our reading
Enforcing safe mutable value semantics (e.g. via borrow-checking) is far easier to do cheaply with a static type system than with a dynamic one.

Their wordsEnsuring that moving, borrowing, and sharing don't break the illusion is surprisingly easy to do with a static type system, and surprisingly hard to do with a dynamic type system, or at least hard to do cheaply.