Hello, I am quite a newbie to Crystal. On many aspects, I find that its design is very smart. But one thing really hurts me: its type-checking is not compositional. Let me detail this on the following example: def demo(c : Class) : Nil a = c.new() puts("demo on #{a.class}") (1..10).each {|x|…

[image] boulme: demo(Array(Bool)) I am not sure to understand why you try to push an Int value inside an Array of Bool But anyway, the raised error by the compiler is quite clear. What do you try to explain ?

I am trying to say that, on the contrary to most strongly-typed languages, Crystal type-checker does not check the definitions of methods, but only their call. As a consequence, this makes debugging harder. Consider this second example, this is only when you decomment line pay(1000) that you find t…

I got you now thank you. I agree with you, it’s something I find a bit annoying with crystal too

[image] boulme: In all other strongly-type language that I know Yea, my 2 cents on this is Crystal is somewhat unique in this regard. Types are not (always) required like they are in other strongly-typed languages. E.g. in you example the Class restriction is essentially not doing anything an…

[image] Blacksmoke16: This provides a lot of flexibility in that you can just write you code and the compiler will figure it out and feel more dynamic, while still preventing you from actually hitting a runtime error like you would in Ruby/Python/PHP. Yes, as far as I understand, Crystal give…

[image] Blacksmoke16: To me it just shows that static typing can only provide so much safety and isn’t an excuse to just not write tests that would have caught this, and asserted it’s doing what you expect. I completely agree. But, strong static typing avoids the pain to write many dummy tes…

Maybe this is just a misunderstanding about how typing in Crystal works. Crystal uses strong static typing. But it works as a kind of static duck typing. The type system does not prevent you from calling a method that is not part of the restricted type’s interface. As long as the actual type imple…

The Earth’s ecosystem is vast, and in a zoo you can even see animals like the platypus. Objective-C #import <Foundation/Foundation.h> void pay(int x) { if (x < 0) { [NSObject bug:x]; // not defined } } int main() { @autoreleasepool { NSLog(@"Hello!"); // pay(10…

[image] straight-shoota: Maybe this is just a misunderstanding about how typing in Crystal works. Crystal uses strong static typing. But it works as a kind of static duck typing. I understand that Crystal type-checker works this way. What I don’t well-understand is that you prefer duck typin…

Incremental static typechecking

Crystal Contrib

ysbaddaden October 16, 2025, 6:09pm 8

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Incremental static typechecking

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