John Carmack on mutable variables

> Making almost every variable const at initialization is good practice. I wish it was the default, and mutable was a keyword.

It's funny how functional programming is slowly becoming the best practice for modern code (pure functions, no side-effects), yet functional programming languages are still considered fringe tech for some reason.

If you want a language where const is the default and mutable is a keyword, try F# for starters. I switched and never looked back.

> If you want a language where const is the default and mutable is a keyword, try F# for starters. I switched and never looked back.

Rust is also like this (let x = 5; / let mut x = 5;).

Or you can also use javascript, typescript and zig like this. Just default to declaring variables with const instead of let / var.

Or swift, which has let (const) vs var (mutable).

FP got there first, but you don't need to use F# to have variables default to constants. Just use almost any language newer than C++.

Are there languages that automatically extend this to things like data structure members? One of the things I like about the C++ const keyword is that if you declare an instance of a struct/class as const it extends that to its members. If the instance isn’t const, you can still mutate them (as long as they aren’t declared const within the structure itself)

Rust works this way, yes. There are escape hatches though, which allow interior mutability.