Restricting type values in a union | TypeScript Community | Page 1

harsh egret May 31, 2024, 7:29 PM

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I am having trouble wording this, however I have this:

//type ApplicationCommandData = UserApplicationCommandData | MessageApplicationCommandData | ChatInputApplicationCommandData
// (from discord.js)

type Foo = ApplicationCommandData | Bar;

interface Bar extends ChatInputApplicationCommandData {
  options?: readonly Exclude<
    ApplicationCommandOptionData,
    {
      type:
        | ApplicationCommandOptionType.SubcommandGroup
        | ApplicationCommandOptionType.Subcommand;
    }
  >[];
  handler(interaction: ChatInputCommandInteraction): Promise<void> | void;
}

function defineFoo(foo: Foo) {
  return foo;
}

defineFoo({
  name: "test",
  description: "test",
  options: [
    {
      type: ApplicationCommandOptionType.SubcommandGroup,
      name: "test",
      description: "test",
      options: [],
    },
  ],
  handler(interaction) {},
});

Why is options allowed to have SubcommandGroup, when Bar is the only type with handler() and it does not allow SubcommandGroup?

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The options for ChatInputApplicationCommandData is readonly ApplicationCommandOptionData[], but shouldn't it be the excluded version because it has the handler that matches Bar?

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It works fine when you change defineFoo(foo: Foo) to defineFoo(foo: Bar) but I want the option to do the original ChatInputApplicationCommandData and my Bar

pallid cedar May 31, 2024, 7:37 PM

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It's a lot easier if you make a TS Playground

sterile gyroBOT May 31, 2024, 7:38 PM

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sandiford#0

Playground Link

Preview:```ts
interface ApplicationCommandData {
a: string
b: string
}

type Foo = ApplicationCommandData | Bar

interface Bar extends ChatInputApplicationCommandData {
options?: readonly Exclude<
ApplicationCommandOptionData,
{
type:
| ApplicationCommandOptionType.SubcommandGroup
...```

pallid cedar May 31, 2024, 7:38 PM

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You can fill in the gaps and then copy the address and paste back here

rotund epoch May 31, 2024, 7:38 PM

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i already did the work 😅:

sterile gyroBOT May 31, 2024, 7:38 PM

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mkantor#0

Playground Link

Preview:```ts
import {
ApplicationCommandData,
ChatInputApplicationCommandData,
ApplicationCommandOptionData,
ApplicationCommandOptionType,
ChatInputCommandInteraction,
} from "discord.js"

type Foo = ApplicationCommandData | Bar

interface Bar extends ChatInputApplicationCommandData {
op
...```

pallid cedar May 31, 2024, 7:39 PM

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lol

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Oh it's all Discord

harsh egret May 31, 2024, 7:39 PM

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😂 Wasnt sure how to do the imports haha

pallid cedar May 31, 2024, 7:39 PM

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Is it a type subtraction issue?

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I guess mkantor will solve it 🙂

rotund epoch May 31, 2024, 7:40 PM

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Why is options allowed to have SubcommandGroup, when Bar is the only type with handler() and it does not allow SubcommandGroup?
the technical answer to this is that excess properties are generally fine. the warning you get for them is very conservative and only kicks in when TS is 100% certain the property can never be accessed

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here's a much simpler/more-self-contained example:

sterile gyroBOT May 31, 2024, 7:42 PM

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type A = { a: true }
type B = { b: true }

function gimmeAOrB(x: A | B) {}

// no error:
gimmeAOrB({
  a: true,
  b: true,
})

harsh egret May 31, 2024, 7:42 PM

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That is cursed. 😭

rotund epoch May 31, 2024, 7:42 PM

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why? there's no problem with having a value that is assignable to both A and B

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or in your case, ApplicationCommandData and Bar

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is there a specific problem this is causing you? like does the presence of handler break something elsewhere?

harsh egret May 31, 2024, 7:44 PM

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If a discord command has a sub group or subcommand, the root command is not possible to be called.

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Just preventing to define a handler that will never be called.

pallid cedar May 31, 2024, 7:46 PM

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You can set handler?: never on the union members that can't have a handler

rotund epoch May 31, 2024, 7:46 PM

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yeah, but i generally would not bother. values in TS can always have excess properties. it's just part of the nature of the type system. IMO it's better to embrace/expect it

harsh egret May 31, 2024, 7:47 PM

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pallid cedar You can set `handler?: never` on the union members that can't have a handler

This make sense, but what would the difference between never and undefined here?

pallid cedar May 31, 2024, 7:47 PM

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harsh egret Just preventing to define a handler that will never be called.

never can't be fulfilled, so it requires that the property is not set.

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You can use undefined if you want to

harsh egret May 31, 2024, 7:47 PM

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ah

rotund epoch May 31, 2024, 7:48 PM

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pallid cedar never can't be fulfilled, so it requires that the property is not set.

(if exactOptionalPropertyTypes is enabled)

harsh egret May 31, 2024, 7:48 PM

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Funnily enough I was ALMOST there

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Just didnt specify that handler should not be defined, I just left it out 😂

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But that works! Thanks!

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!resolved

pallid cedar May 31, 2024, 7:52 PM

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I actually started working on implementing closed/exact types in TypeScript

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I don't know if the maintainers would actually add it if completed though.

harsh egret May 31, 2024, 7:54 PM

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Wizard! 🪄

pallid cedar May 31, 2024, 7:54 PM

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tsc is surprisingly simply to work on really

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It took me 2-3 days to do that, with no prior experience.

#Restricting type values in a union