Is there benefit of using this branded type over just encapsulating the raw string in a private variable in closure or class? This feels a bit like forced nominal typing. The Email type doesn't have to be a string, it can be encapsulated so that invalid Emails are not representable.
Zod is by far the most ergonomic way to express those ideas in TypeScript these days. I miss it when writing code in other languages.
The friction with the rest of the ecosystem is real, though. Most code out there expects you to handle errors with exceptions.
I get the impression that polymorphic return types could get in the way of JSC/V8/SpiderMonkey's JIT, but I haven't measured it and I'm not sure of the actual impact on hot and cold paths. Same for all the allocations caused by custom Option<T>/Result<T,E> implementations.
I think using Zod at the edge (with branded types and whatnot), while keeping return types as T/Promise<T> to keep a sane relationship with the ecosystem is a good middle ground.
Meta: in addition to upvotes and downvotes, we almost need a slop/not-slop slider.
This one barely scrapes by at what feels like 30-40% "slop": "honestly", "the one thing", etc...
...but I did learn something about "Brand" types, and have personally tried to do more of "parse don't validate" in my own code.
Recently I did this similar trick for `exec( ValidExecutable(...) )` [python], where it required tagging/washing through a private function/variable to "get" the private bit.
All the scanners tend to light up when they see "exec" at all (eg: `exec( "pandoc" )` for PDF generation), but I needed to hard code a few "expected" pandoc locations so the imaginary hackers couldn't shadow "pandoc" on a path location they controlled.
This feels right, and I also have never done it (or had the guts to get others to do it).
The reason I've not is - say there's an optional field. Currently we call that null, probably, and check each time if it's there or not. I could instead make a type, like User and UserWithPhoneNumber. Should we be making types for each combination of present/absent fields? That can't be right.
The classic answer is to move the logic inside the domain object, or have a helper function outside the object, so you aren't constantly checking for field presence/absence, but are instead writing the logic once and calling some code.
I'm not sure in practice types can help with this. But I'd love to be proven wrong.
I think this is a slightly different problem. The absence of an optional field, if that's a legal state, is meaningful every time you use the type, so you encode it on the field: `phone: ValidPhoneNumber | null`. When it's not null you're still guaranteed a valid phone number. When it is null, that's a legal state you have to handle and which is domain logic, not validation you forgot to do.
The combinatorial explosion you're picturing only shows up if you make a separate type per combination of present fields, but you don't need to. An independent optional field stays one `T | null`. You only reach for distinct types when fields are correlated and present together because they represent a state, and then it's a discriminated union on a status field, which is N states, not 2^N.
This explosion of optionality types is (the most important) topic of Rich Hickey's "Maybe Not" talk. I recommend it!
The short version is: the shape of a type is inherent to the type itself, but the optionality of its members is dependent on the situation. A type system that solves this problem separates these concepts to allow for this distinction.
I _suspect_ it's possible to implement something like that in typescript but I haven't tried it myself (and I doubt it's very ergonomic).
One of the pillars of Domain Driven Design. I love working on a pure DDD application but I do not often convince my team (I am a constant) that this is the best way ...
As a new TypeScript user these are concepts that have greatly helped me simplify my code and improve reliability discrete of testing. Many LLMs guide in this direction if you loosely ask them, but having a concise post like this with the what and the why is fantastic as reference material. The suggestion to use Separation and a Linter rule is something I'm going to immediately look into for my current project. Great post!
The friction with the rest of the ecosystem is real, though. Most code out there expects you to handle errors with exceptions.
I get the impression that polymorphic return types could get in the way of JSC/V8/SpiderMonkey's JIT, but I haven't measured it and I'm not sure of the actual impact on hot and cold paths. Same for all the allocations caused by custom Option<T>/Result<T,E> implementations.
I think using Zod at the edge (with branded types and whatnot), while keeping return types as T/Promise<T> to keep a sane relationship with the ecosystem is a good middle ground.
If the result is better for having used AI, why wouldn't an author want to disclose it?
This one barely scrapes by at what feels like 30-40% "slop": "honestly", "the one thing", etc...
...but I did learn something about "Brand" types, and have personally tried to do more of "parse don't validate" in my own code.
Recently I did this similar trick for `exec( ValidExecutable(...) )` [python], where it required tagging/washing through a private function/variable to "get" the private bit.
All the scanners tend to light up when they see "exec" at all (eg: `exec( "pandoc" )` for PDF generation), but I needed to hard code a few "expected" pandoc locations so the imaginary hackers couldn't shadow "pandoc" on a path location they controlled.
The reason I've not is - say there's an optional field. Currently we call that null, probably, and check each time if it's there or not. I could instead make a type, like User and UserWithPhoneNumber. Should we be making types for each combination of present/absent fields? That can't be right.
The classic answer is to move the logic inside the domain object, or have a helper function outside the object, so you aren't constantly checking for field presence/absence, but are instead writing the logic once and calling some code.
I'm not sure in practice types can help with this. But I'd love to be proven wrong.
The combinatorial explosion you're picturing only shows up if you make a separate type per combination of present fields, but you don't need to. An independent optional field stays one `T | null`. You only reach for distinct types when fields are correlated and present together because they represent a state, and then it's a discriminated union on a status field, which is N states, not 2^N.
The short version is: the shape of a type is inherent to the type itself, but the optionality of its members is dependent on the situation. A type system that solves this problem separates these concepts to allow for this distinction.
I _suspect_ it's possible to implement something like that in typescript but I haven't tried it myself (and I doubt it's very ergonomic).
It's more about writing
overWhat did you mean by that? You don't accept mutability or any inputs on your state of mind?