I took extensive notes while reading the React Native and React documentation this weekind. I plan to post them after verifying that all code snippets in my notes are correct. Similar to my previous posts, I will try to explain React Native using concepts familiar to SwiftUI developers.
I found a few additional differences in the TypeScript documentation that are not mentioned in the Swift-TypeScript cheatsheet I linked in one of my previous posts:
- The return type of a function can be inferred. If there’s no return type specified in the declaration, it doesn’t mean the function returns
void. - Optionality in TypeScript is implemented at the property level, not in the type system. To make a property optional, add ? at the end of the property name. There are utility types in TypeScript that can change the optionality of properties, such as
Partial<Type>andRequired<Type>. - Use
extendskeyword to add type constraints in generics:<T1, T2 extends T1> - Use
&to “combine” two or more types into one. It will create a new type that contains properties from all combined types. - Use
|to create auniontype that can be one of the types being “united”. - To make illegal states unrepresentable Swift devs often use enums with associated types. To mimic Swift’s
switchonenumwith associated types use union of interfaces representing associated types and add a tag with unique literal types to each interface. Then, useswitchon the tag of union type, that’s enough to guarantee type safety. - For
RawRepresentableenums it’s usually more efficient to use a union of literal types representing values because it doesn’t add extra run-time code like TS’senum. Another alternative isconst enum, but there is something in the TS documentation about potential problems with it. keyofis a way to provide a type for dynamic member lookups. It’s somewhat similar tokeypathin Swift.typeof, when used inside conditions, allows for narrowing the type in a conditional branch.- “Indexed access type” allows to get type of a property by using indexed access syntax:
type ContactID = Contact["id"] - Tuple in TS is a sort of Array type that knows exactly how many elements it contains, and exactly which types it contains at specific positions. Example:
type StringNumberPair = [string, number];describes array whose 0 index contains a string and whose 1 index contains a number. - Resources cleanup in Swift’s
deinitcan be mimicked by adding[Symbol.dispose]()method to a class and then storing created instance withusingkeyword instead of const or let.
During my journey from Swift to TypeScript, I often wonder how developers migrating in the opposite direction feel. What do they appreciate about Swift, and what aspects of TypeScript do they miss?
One of the things I like about Swift is the ability to make illegal states unrepresentable using type system. It looks like something similar is possible in TypeScript using combination of union types and literal types.
So far, Swift-Typescript Cheatsheet dabbott.github.io/webdev-pr… has been the best resource for learning TS for me.
Wednesday, November 13, 2024 →
I’ve been writing native iOS apps using Swift for the last 8 years (and years of ObjC before that). Next week I will start working on a new project with ReactNative and TypeScript. All learning materials I found are written either for web developers or people completely new to programming 🤔