[0]: https://www.typescriptlang.org/play/?#code/C4TwDgpgBAogdgVwL... from StackOverflow[1]
[1]: https://stackoverflow.com/questions/39494689/is-it-possible-...
I think its more useful in a language like rust, because the compiler can use that information to better optimize the emitted assembly.
It starts with the question of how I would like to design my sequences:
- Is it the range (0, 10] in steps of 1?
- Is it the range (0, 2^10) in steps by the power of 2?
- Is it the range (0.0, 2PI] in steps of EPSILON?
How would the compiler engineer generalize this optimization?
And the question would continue whether I'd be really able to define them that precisely before runtime. Most applications are just dealing with lightweight structures, mostly serialized JSON nowadays, and then even there are enough fuck-ups[0] where such an optimization wouldn't help at all.
I can imagine the places where they really matter are some heavy memory intensive data structures like deep neural networks, graphics or video and the like - for the time being they're just dealing with tensors of data type floatX, and that seems to be fine AFAIK.
I mean, I'd be really nice if the smaller memory footprint could come out-of-the-box during compilation. But all the CLI tools written in rust certainly don't have the use case to put this complication on the shoulders of compiler research.
[0]: https://nee.lv/2021/02/28/How-I-cut-GTA-Online-loading-times...
It would be better if the type system could encode types like this directly. Better for ergonomics and better for optimisation.
I think that's less a question whether you can, but rather whether you should or shouldn't design it that way... (I'll use TypeScript here for the simpler syntax)
It'd be perfectly fine to do something like this:
type ColorR = 'red';
type ColorG = 'green';
type ColorB = 'blue';
type ColorRGB = ColorR | ColorG | ColorB;
// constraint A
type ColorGB = ColorG | ColorB;
// constraint B
type ColorGB = Exclude<ColorRGB, ColorR>;
But if you really need to reuse the type ColorGB (probably some categorization other than all the colors), then you'd need to pay close attention to your designed constraint.
Say I have some enum like ColorRGB here. In some contexts, only a limited subset of variants are valid - say, ColorGB. There's a few ways to code this - but they're all - in different ways - horrible:
1. Use ColorRGB in all contexts. Use asserts or something to verify that the value is one of the expected variants. This fails at expressing what I want in the type system - and the code is longer, slower and more error prone as a result.
2. Have two enums, ColorRGB and ColorGB. ColorRGB is defined as enum ColorRGB { Red, Restricted(ColorGB) }. This lets me encode the constraint - since I can use ColorGB explicitly. But it makes Color harder to use - since I need to match out the inner value all over the place.
3. Have two enums, ColorRGB and ColorGB which both have variants for Green and Blue. Implement conversion methods (impl From) between the two types. Now I have two types instead of one. I have conversions between them. And I'll probably end up with duplicate methods & trait impls for ColorRGB and ColorGB.
Luckily this doesn't come up that often. But - as your typescript example shows - it can just be expressed directly in the type system. And LLVM already tracks which variants are possible throughout a function for optimisations' sake. I wish rust had a way to express something like Exclude<ColorRGB, ColorR>.
No.
- In very dynamic languages (like javascript), most types arguably don't have names at all. For example, I can make a function to add 2d vectors together. Even though I can use 2d vectors in my program, there doesn't have to be a 2d vector type. (Eg, const vecAdd = (a, b) => ({x: a.x+b.x, y: a.y+b.y}) ).
- Most modern languages have tuples. And tuples are usually anonymous. For example, in rust I could pass around 2d vectors by simply using tuples of (f64, f64). I can even give my implicit vector type functions via the trait system.
- In typescript you can have whole struct definitions be anonymous if you want to. Eg: const MyComponent(props: {x: number, y: string, ...}) {...}.
- There's also lots of types in languages like typescript and rust which are unfortunately impossible to name. For example, if I have this code:
Arguably, c is a Color object. But actually, c must be either Color::Green or Color::Blue. The compiler understands this and uses it in lots of little ways. But unfortunately we can't actually name the restricted type in the program.Rust can do the same thing with integers - even though (weirdly) it has no way to name an integer in a restricted range. For example, in this code the compiler knows that y must be less than 256 - so the if statement is always false, and it skips the if statement entirely:
https://rust.godbolt.org/z/3nTrabnYz
But - its impossible to write a function that takes as input an integer that must be within some arbitrary range.