Most modern typed languages support encoding this information in the type of the variable, so that the compiler catches it, instead of in the variable name. Alexis King wrote a blog post about it that reached the front page a few days ago.
https://lexi-lambda.github.io/blog/2019/11/05/parse-don-t-va...
Yes, though the notation approach is worth following if you cannot use the type system (lang doesn't support it, or incurs unacceptable performance or complexity overhead).
But yeah, zero cost compiler magic is the reason Rust is so good.
> GALAXY BRAIN: Apps Hungarian is stupid and just duplicates the work of the type system
Is this correct? From the article, Apps Hungarian represents your intent for the var (the kind), not the type. Systems Hungarian represents the type (duplicative).
He meant that the intent (kind) can be factored into the type system too. Instead of using type string for both “unsafe string” kind and “safe string” kind, you’d use two different types. So the type system aka compiler can catch a mistake, in addition to your eyes.
I currently use a mix of thin typedefs (using ClockT = uint32_t, the compiler doesn't catch mixups) and putting units in variable names. I've used this approach in Python, Rust, and C++, and in over 1 year have had zero bugs that could've been caught via compiler-enforced units. (I don't know if this approach will work for others though.)
I've tried using a unit system library in Rust, for audio programming. It was not worth it for me. I had to define types for clock cycles, audio sample durations, and amplitudes. Then cycles per second and samples per second were expressed as ratios. Then you need (cycle / second) to have type (cycles per second). The typenum-based error messages were dreadful. And also you sometimes need to use different base numeric types used to store these dimensioned quantities. And also write extra typecasts to box and unbox between unit-wrapped quantities and plain integers.
> No compiler can know that a string variable is a "name" or a "password".
In pretty much any language supporting user-defined types and/or type aliases, types can be used for that information (with aliases, providing documentation the same as hungarian notation does; with real types, providing the possibility for enforced protection against accidental misuse.)
But the article doesn't actually use hungarian notation for that kind of thing, it uses it for traits that are not "what it does", but instead metadata analogous to Ruby's "taint". Which, again, is something easily encoded in typing, in a static language, either as a core feature of typing or via user-defined (possibly wrapper, depending on other features of the type system or general language semantics) types; type aliases, even, would work as well as hungarian notation, but using actual types lets you put guarantees in place rather than just providing documentation.
It still might be possible to have types like `UserId` or `UserCredential`, which get parsed at the request time and never roll back to plain strings. It is evident that they are indeed different subtypes of strings: user identifiers can't have a space for example.
That said, I generally agree that conventional type systems are not (yet) capable of encoding all those informations to a type. I prefer a mix of actual types and coding conventions for the practical matter.
As a thought experiment, I like to assume that there is a hypothetical language where everything is encoded in types, to the point where you don't have or need variable names anymore. Every typed language (and programming style) we use is some point in the spectrum of practical compromises between that hypothetical language where all pre-runtime information is in formal types and scripting languages where all pre-runtime information is in informal names.
Java for example has to leave quite a lot of that information in names because there are no type aliases and final types exist.
I'm curious what type of capabilities are lacking in the Ada or the F# type system to handle this. You can create 'new' (hear incompatible) types instead of subtypes and they won't be affectable to each other. So
type User_Id_Type is new String;
type User_Credential_Type is new String;
Then in your request deserializer convert once from String to the correct type, and at the use site only allow taking the correct type?
You can also add static predicates to ensure User_Id_Type doesn't contain spaces. You can also make the type 'opaque' and it won't be possible to convert to a String without a bespoke interface.
I'm not sure what's missing. I almost feel like it would be a great challenge :-)
I think in this particular case they suffice, because they are clearly different subtypes as I've mentioned.
It is much harder, if not impossible, if you have to describe a relation between two or more values of the same subtypes. For example, imagine that you already "know" certain indices never go off the boundary of given array but want to encode that information to types. Sure, there exists a Rust crate [1] that tracks a relation between indices and originating array via lifetime, but it is complicated.
Mmmh thanks for the link and the paper about generative types. Seems very interesting!
I'm wondering if using type predicates or type invariants (+ proof for static verification, otherwise the check will mostly be at runtime) would help here.
Hungarian notation solves one problem: it makes wrong code look wrong.
Type alias can also do that, but they can do so in a way where correctness can be statically enforced.
As an example, let’s say you have a Write function like in the article, but it only takes an HTMLString, which can’t implicitly be casted from String. Then, you can have Encode return an HTMLString, but take a String. Finally, you can use static analysis to only allow whitelisted functions to construct non-literal HTMLStrings (so anyone could do a literal of HTML, but every other usage would require encoding or whitelisting.)
This is a bit rudimentary of an example, but it is widely used in practice.
It may sounds a hassle but you only have to handle it at the interfaces (for example for a web app in the controller and data layer), in the rest of the code you just manipulate your value like any other type.
But type is a machine-readable way to say what a variable does or is. A compiler can certainly know a name from a password if its type support is versatile enough and you use separate types for them. Or, for example, for things like "unchecked C string", "valid UTF-8 C string", "NKFD-normalized UTF-8 C string", etc. A separate type for password may be a jolly good idea with a logging system you can dump any data to; you certainly wouldn't want it to log passwords.
Using prefixes is a poor man's type system, a loose convention to be enforced by humans, while with types it would be a machine-readable and enforceable requirement.
