Exploring Immutable-by-Default TypeScript: A Technical Experiment
By
ingve
Hand-rolled, kettle-boiled, baked to perfection. Worth every minute at the bakery.
Summary
A developer explores whether it's possible to make TypeScript immutable by default without modifying the language itself, similar to Rust's approach where variables are immutable unless explicitly declared mutable. The author attempts to implement this purely through TypeScript's type system, successfully achieving immutability for arrays and records but encountering challenges with regular objects. The article documents the technical exploration and limitations of this approach.
Key quotes
· 5 pulledI like programming languages where variables are immutable by default. For example, in Rust, let declares an immutable variable and let mut declares a mutable one.
I've long wanted this in other languages, like TypeScript, which is mutable by default—the opposite of what I want!
My goal was to do this purely with TypeScript, without changing TypeScript itself. That meant no lint rules or other tools.
I spent an evening trying to make TypeScript values immutable by default.
I got it working with arrays and records, but couldn't make it work for regular objects.
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