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What do you mean by dynamically-typed generics and statically typed generics here? I've looked up "post-monomorphization errors" and found some things about ass

What do you mean by dynamically-typed generics and statically typed generics here? I've looked up "post-monomorphization errors" and found some things about assertions about generic types failing because of the choices made by the user who passed in types or constants that do not work with the generic code. It seems like Zig libraries have the option of generating the errors at the right place if they place their assertions in the function that returns the type to the user, but they also have the option of generating the errors in the wrong place if they place their assertions in methods of the type. > So… I’m not sold on your wording that it’s circumventing issues, as it’s choosing a different set of trade-offs. In shedding types-are-a-language-of-their-own, you also shed confidence about what’s a breaking change, and make call sites more fragile. Decide for yourself whether it’s worth it. Client code can just look at all the members of all the structs so there's not really much hope for enforcing that changes cannot break any client code using compiler-adjacent tooling.

chrismorgan 3y ago
It’s easiest to see the distinction in otherwise-similar systems, so I’ll choose Rust generics (statically-typed) and C++ templates (dynamically-typed). In Rust, the generic constraints (the traits that the type must satisfy) are a contract, part of the signature. The caller must satisfy them, and then the callee knows nothing else about the type it has received. Therefore, changes inside the body of the generic method will never† cause any code that uses the function to stop compiling. In C++, templates don’t have that, so you have to seek knowledge of what conditions your type must satisfy some other way, and it’s easy to accidentally depend on additional details (since it’s not statically checked), so that changes in the template that you thought were harmless actually break someone else’s code somewhere else that uses your template in ways you didn’t expect. https://gist.github.com/brendanzab/9220415 https://gist.github.com/brendanzab/9220415 has a decent example, though it’s from 2014 and refers to Zero and One traits that were removed from the standard library before Rust 1.0, and the compiler messages would be better today as well. —⁂— † In practice there’s at least one way of leaking details, so post-monomorphisation errors that aren’t compiler bugs can actually happen, though it’s very rare: if you return an `impl Trait`, the body leaks whether it implements auto traits like Send.

chrismorgan 3y ago

It’s easiest to see the distinction in otherwise-similar systems, so I’ll choose Rust generics (statically-typed) and C++ templates (dynamically-typed). In Rust, the generic constraints (the traits that the type must satisfy) are a contract, part of the signature. The caller must satisfy them, and then the callee knows nothing else about the type it has received. Therefore, changes inside the body of the generic method will never† cause any code that uses the function to stop compiling. In C++, templates don’t have that, so you have to seek knowledge of what conditions your type must satisfy some other way, and it’s easy to accidentally depend on additional details (since it’s not statically checked), so that changes in the template that you thought were harmless actually break someone else’s code somewhere else that uses your template in ways you didn’t expect. https://gist.github.com/brendanzab/9220415 https://gist.github.com/brendanzab/9220415 has a decent example, though it’s from 2014 and refers to Zero and One traits that were removed from the standard library before Rust 1.0, and the compiler messages would be better today as well. —⁂— † In practice there’s at least one way of leaking details, so post-monomorphisation errors that aren’t compiler bugs can actually happen, though it’s very rare: if you return an `impl Trait`, the body leaks whether it implements auto traits like Send.