alt Hacker News> Mutability
> By default, variables are mutable. You can enable Immutable by Default mode using a directive.
> //> immutable-by-default
> var x = 10; > // x = 20; // Error: x is immutable
> var mut y = 10; > y = 20; // OK
Wait, but this means that if I’m reading somebody’s code, I won’t know if variables are mutable or not unless I read the whole file looking for such directive. Imagine if someone even defined custom directives, that doesn’t make it readable.
Replies
It's not ideal but it seems like something an LSP could tell you on a hover event. I didn't see an LSP (I didn't look that hard either) but presumably that's within the scope of their mission statement to deliver modern language ergonomics. (But I agree with sibling comments that this should be a keyword. Another decent alternative would be that it's only global in scope.)
Other languages also have non-local qays of influencing compiler behavior, for example attributes in rust (standard) or compiler pragmas in C (non-standard).
When reading working code, it doesn't matter whether the language mode allows variable reassignment. It only matters when you want to change it. And even then, the compiler will yell at you when you do the wrong thing. Testing it out is probably much faster than searching the codebase for a directive. It doesn't seem like a big deal to me.
Yeah, immutability should probably use a `let` keyword and compiler analysis should enforce value semantics on those declarations.
Given an option that is configurable, why would the default setting be the one that increases probability of errors?
For some niches the answer is "because the convenience is worth it" (e.g. game jams). But I personally think the error prone option should be opt in for such cases.
Or to be blunt: correctness should not be opt-in. It should be opt-out.
I have considered such a flag for my future language, which I named #explode-randomly-at-runtime ;)