It's crazy the amount of work that is spent to essentially implement static typing into dynamically / duck typed languages.
Projects like this, mypy and others makes the whole thing bizarre to say the least.
Projects like this, mypy and others makes the whole thing bizarre to say the least.
If your program produces or consumes JSON _and_ you think it would be a good idea to ensure said JSON is what you are/a client is expecting, then you need something like this in any implementation language.
what I completely don't understand is the current fad on everything-should-be-yaml where yaml is marginally easier to write than XML, a tiny bit more than marginally easier to read (caveat emptor - Norway has a country code) and otherwise exactly as broken. (i'm talking about the 'safe' variant.)
- I was afraid it would change the language culture
- It was not comfortable to use
- The idea and design was, as you said, bizarre
- Use use a dynamic language, why the hell would I want that?
Years after the fact, I'm really happy about it.
First, most of my Python code don't use them, so Python stays python. But if I ever need them, there are here.
Of course, you could argue I should just use a language that has been designed for that since I need type. But that's missing the point: I don't usually start using hints. I code regular Python, because it's awesome. I just sometimes add type hints after the fact as a bonus.
The ability to do that is fantastic, even if the type system is far from perfect.
I want to code with Python most of the time anyway. I personally have very few use cases for another language, doing mostly web stuff.
Type hints are still very verbose, and convoluted, although it will get better with 3.9 thanks to 2 PEP targeting type hints ergonomics. So sure, it's never going to fit perfectly, but I'm glad it's here.
Now for a JSON schema, I guess it's the same deal. You use JSON because it fits your use case, and one day you realize your situation could now benefit from more robustness, and you add it to the mix.
Again, you could argue you should have though of that at the beginning, but projects don't have frozen requirements, they evolve. And often, you want to start lean, because it will most probably stays that way, and otherwise would be so costly the project would never grow to a point you would need robustness.
Now in this particular case, this lib is not just checking type, but also arbitrary logic. And making sure data is consistent is necessary no matter how dynamic or static your language is. There is a limit to the constraints your type system can represent.
Type inference can get you so so far
But then again, Django as well.
What's different this and Python type hints is that this was a public-facing API, so you have far less control over what data you'll see, and the server code was Java, so getting things strongly typed and validated early on makes your life easier.
My point is, I'd rather have a not so perfect one when I need it, that None at all.
And most of the time I don't need one.
I mean the attitude that Python is "good enough" because it has type hinting and therefore it is not worth bothering with exploring other languages, especially ones that have wholly more powerful type systems. I have found (personal experience only here) that it can be tremendously hard to get Python programmers to learn and embrace other languages and approaches to software.
I think that would be a great feature but from what I see static typing fails here, too.
(s/def ::number #(<= -180 % 180))
(s/def ::my-string (s/and string? #(re-matches #"[a-zA-Z0-9]*" %)))NB Last time I used Pascal was probably 35 years ago....
Edit: I would suspect Ada would have something like this.
Pretty much all of them. Any simple predicate like this can be encoded with witness types.
Here's an example in Java, which is hardly the paragon of static typing (i.e. it's no Haskell/Idris/Agda/Rust/Typescript):
class AlphaNumericString {
private final String str;
// use a fallible factory with a `private` constructor if you're
// morally opposed to exceptions
public AlphaNumericString(String str) throws AlphaNumericException {
if (!str.matches("^[a-zA-Z0-9]*$")) {
throw new AlphaNumericException();
}
this.str = str;
}
private static class AlphaNumericException extends Exception {
}
}
You may object and say that newtype wrapping is cumbersome but:
1. That's an argument about sugar and ergonomics, not about the semantics that the static type system enforces
2. Some languages make it easier to generate forwarding methods to the underlying type (a la https://kotlinlang.org/docs/reference/delegation.html)
3. The `AlphaNumericString` is describing a smaller set of values than `String`. In general, you should be strongly considering the methods you allow and make sure that all paths continue to enforce the semantics you intend.