type-fest VS newtype-ts

Related: https://github.com/sindresorhus/type-fest/blob/main/source/o...

Typescript doesn’t natively provide an Opaque type that we can use to define a string that has already been localized. If the data looks like a string, Typescript will consider it a string. We can however use utility types that simulate opaque types, like the Opaque definition in type-fest:

With these powerful features, you can create dynamic and expressive types. One last thing I want to mention before moving on, is that you can install libraries with which you can add more types to your project like type-fest or utility-types. These libraries contain a lot of useful types that you can use in your project.

Also, it’s not as restrictive as mutability tools — if you know what you are doing and want to ignore this limitation for a particular case, you can apply the -readonly modifier or the Writeable type from type-fest or ts-essentials.

Remember you can derive one type from another type so you can make sure they don't diverge. SetOptional type util

Some folks have built whole SQL databases and DSL compilers in the TS type system. These tend to be toy projects with disclaimers not to use them. But the type system being Turing complete[0] (for better or worse), pretty much whatever you can imagine. This project[1] is one I actually return to frequently for practical ideas.

0: https://github.com/microsoft/TypeScript/issues/14833

1: https://github.com/sindresorhus/type-fest

Have a look at SetRequired and SetOptional in type-fest

Try the Exact method provided by Type Fest, looks like it does what you're looking for

This is a fairly common scenario and available via libraries like type-fest or implementable with a couple lines of code.

Curious what your issue was with duck-typing. Were you effectively looking to create ADTs that are required to go through a specific step-by-step process, not simply 'look like' the thing that was expected?

If so, you might be interested in [newtype-ts].

[newtype-ts]: https://github.com/gcanti/newtype-ts

this one https://github.com/gcanti/newtype-ts ?

You don't need classes for nominal types: https://github.com/gcanti/newtype-ts

Creating newtypes (via newtype-ts) for fractions and percentages is worthwhile if you're very concerned about correctness, though it's unfortunate that absent typeclasses they're not terribly ergonomic.

I haven't used this library in particular or this one, but bless the authors and all the others for trying to make it happen… the project I'm now leading uses strongly typed strings for different component addresses, and it saves me to constantly look up the documentation what the functions need – it's beautiful.

A "nominal" solution with no runtime overhead can be provided by branded types, other words for this are "opaque types" or "newtypes". Some libraries like newtype-ts exist to help with the construction of these. That library README describes it as:

You can also look at the fp-ts ecosystem for inspiration. newtype-ts and io-ts's Branded type with io-ts-type's UUID as a good example

Alternatively we can use other more sophisticated techniques to achieve nominal typing or libraries such as: newtype-ts or io-ts.

One using fp-ts and newtype-ts

We are going to use newtype-ts to build a branded type: