Mapped keyof types to class | TypeScript Community | Page 1

agile cape Mar 9, 2023, 1:43 AM

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how do I write a version of this code that actually works

interface ID {
  id: string;
}

export class BaseClientEntity<T extends ID> {
  [key: keyof T]: T[key];
  constructor(base: T) {
    for (const key in base) {
      if (base.hasOwnProperty(key)) {
        (this as any)[key] = base[key];
      }
    }
  }
}

pseudo sable Mar 9, 2023, 1:50 AM

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don't use loops / reduction functions to copy / transform key/values from an object

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because it's not that easy to type

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because you'd need to declare an empty object first
but then you wouldn't be able to assign keys/values to an empty object

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if you make it partial, then you still need to remove the partial before retning it, etc.

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so it's not that easy

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I recommend using Object.entries(), Array.prototype.map(), and Object.fromEntries()

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so that's for the assignment part

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about this part, [key: keyof T]: T[key];, you can just use implements to implement an interface

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just like in regular OOP

ember fiberBOT Mar 9, 2023, 1:55 AM

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Ascor8522#7606

Playground Link

Preview:```ts
interface ID {
id: string
}

export class BaseClientEntity implements ID {
id!: string

constructor(baseClientEntity: {id: string}) {
Object.assign(this, baseClientEntity)
}
}```

pseudo sable Mar 9, 2023, 1:55 AM

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but that means you'll have to repeat some code

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@agile cape

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one thing you could do, is use an abstract class that you will inherit from

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that way, you'll have a separate ID type, while not having to repeat those fields

ember fiberBOT Mar 9, 2023, 1:57 AM

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Ascor8522#7606

Playground Link

Preview:```ts
abstract class ID {
id!: string

constructor(id: {id: string}) {
Object.assign(this, id)
}
}

export class BaseClientEntity extends ID {
constructor(baseClientEntity: {id: string}) {
super(baseClientEntity)
Object.assign(this, baseClientEntit
...```

pseudo sable Mar 9, 2023, 1:57 AM

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like so

agile cape Mar 9, 2023, 1:57 AM

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ok

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lemme try this

agile cape Mar 9, 2023, 1:58 AM

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pseudo sable about this part, `[key: keyof T]: T[key];`, you can just use `implements` to imp...

that's how I've been doing that, I guess

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but you need to repeat everything from the interface into the every version of it

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and there's a lot of it

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a decent chunk of it is generated code

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so it's not always BaseClientEntity extends ID

pseudo sable Mar 9, 2023, 1:59 AM

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hence my 2nd solution

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but yeah, there is no easy fix

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maybe if you provide more context I'm sure we can work out a better solution

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but yeah, mixing raw types and classes in TS is always a bit of a pain

agile cape Mar 9, 2023, 2:00 AM

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I basically have a bunch of plain interfaces generated

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I want to "augment" them into classes

pseudo sable Mar 9, 2023, 2:01 AM

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and combining types/interfaces together is easier and provides as much safety

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just create classes in the first place

agile cape Mar 9, 2023, 2:01 AM

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not possible

pseudo sable Mar 9, 2023, 2:01 AM

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no reason to use interfaces as DTO in TS, you can use clases to achieve the same thing

agile cape Mar 9, 2023, 2:01 AM

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again, a decent chunk of it is generated by a code generation tool

pseudo sable Mar 9, 2023, 2:02 AM

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then don't use classes

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but raw objects

agile cape Mar 9, 2023, 2:02 AM

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fair

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but less ergonomics

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I guess I can redesign my APIs

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I feel like a main issue with TypeScript that many people haven't noticed is that typescript usually maintains a good separation of values and types

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except for classes

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they're values

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but also types

pseudo sable Mar 9, 2023, 2:06 AM

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typescript usually maintains a good separation of values and types
don't really see what you mean by that

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except for classes
they're values
but also types
the fact an object is a class doesn't matter at all in TS
only it's "general shape" matters

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structural typing in a nutshell

agile cape Mar 9, 2023, 2:08 AM

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pseudo sable > typescript usually maintains a good separation of values and types don't reall...

const n = 123
console.log(n) // works
type Bleh = Foo<n> // doesn't work

type t = { foo: string }
console.log(t) // doesn't work
type Bleh = Foo<t> // works

class c {}
console.log(c) // works
type Bleh = Foo<c> // also works

pseudo sable Mar 9, 2023, 2:09 AM

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right, there is a difference between a JS object you can use (value)

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and a TS type that will be erased and that can only be used to check your code

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however, there are ways to create types from values

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like typeof

agile cape Mar 9, 2023, 2:10 AM

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yeah

pseudo sable Mar 9, 2023, 2:10 AM

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const foo = 123;
type Foo = typeof foo;
//   ^?

agile cape Mar 9, 2023, 2:10 AM

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do types live in the same namespace as values

pseudo sable Mar 9, 2023, 2:11 AM

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yes, no reason to keep them separate

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they are related after all

agile cape Mar 9, 2023, 2:11 AM

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would something like

const Foo = 123;
type Foo = typeof Foo;

work

pseudo sable Mar 9, 2023, 2:11 AM

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no, can't use the same name

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and please, variables should be camelCase in JS/TS

agile cape Mar 9, 2023, 2:12 AM

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I know that

agile cape Mar 9, 2023, 2:13 AM

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pseudo sable no, can't use the same name

just tried it, it apparently works

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I was just asking this as an example to ask if it's possible for the types and values to have a same name

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if you think about it, that's what classes are

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they declare a type with the same name as the value

pseudo sable Mar 9, 2023, 2:14 AM

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right, you can merge a variable and a type together

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but would not recommend

agile cape Mar 9, 2023, 2:14 AM

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yeah

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sounds painful

pseudo sable Mar 9, 2023, 2:15 AM

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if you think about it, that's what classes are
they declare a type with the same name as the value
right, the same name can be used both to create new instances and to refer to the type of an instance

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and to refer to the type of the class itself, have to use typeof

agile cape Mar 9, 2023, 2:16 AM

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ok, so from what I see here I shouldn't try to augment interfaces to classes

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but just use classes outright

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or interfaces

pseudo sable Mar 9, 2023, 2:18 AM

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yes, either of those

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but combining them will be kind of a pain

agile cape Mar 9, 2023, 2:18 AM

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I'm just basing my designs off how discord.js and similar libraries are built

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they cache heavily

pseudo sable Mar 9, 2023, 2:19 AM

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especially if you want to use classes instances for their class "properties" (instanceof + methods + inheritance)

agile cape Mar 9, 2023, 2:19 AM

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and it's generally a mess

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I just want a way to implement an interface without repeating myself too much

pseudo sable Mar 9, 2023, 2:20 AM

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right, it becomes more about keeping track of where the data is, and in what state it is, if it needs to be re-validated or not, etc.

agile cape Mar 9, 2023, 2:20 AM

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https://stackoverflow.com/questions/65787571/avoiding-fields-declaration-duplication-in-interface-and-class-definition

Stack Overflow

Avoiding fields declaration duplication in interface and class defi...

I have an interface like
interface I {
a : string;
b : number;
c : string;
}
And now I'm declaring a class which will have public members a, b, c as per the interface I.
So I declare
class C

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it is possible

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again, type merging the interface with the class

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so can't really be checked properly by the compiler

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but still, much of what is here is for internal library code

agile cape Mar 9, 2023, 2:22 AM

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pseudo sable right, it becomes more about keeping track of where the data is, and in what sta...

I basically built up an internal library to do exactly that automatically for me